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Biomedical subjects

T M Scott

Publications and source records attributed to T M Scott.

At least 55 records · Page 3Linked to original sources
PubMed1986

An examination of the evidence for the existence of preformed pathways in the neural tube of Xenopus laevis.

We have examined the neural tube in Xenopus laevis tadpoles to investigate the anatomical guidance elements which may be present in the presumptive marginal zone. With appropriate fixation protocols the neuroepithelial cells appeared in contact; electron microscopic observations failed to show any specialized intercellular spaces preceding the growing axons. The first fibres were found in the intercellular clefts between the neuroepithelial cells near the surface of the neural tube. Reconstructions of the neural tube from examination of serial 1 micron sections showed that the intercellular clefts are non-aligned at this stage and branching. Scanning electron microscopy of the surface of the neural tube confirmed that the intercellular spaces are non-aligned and often branch caudal to the growing front of descending axons. Thus to grow in a consistent direction the developing axons may have to make consistent and selective (specific) selections of pathway at numerous branch points if their growth is restricted to these intercellular clefts. As more axons grow along the neural tube, the intercellular clefts become wider, and the neuroepithelial cells bounding the clefts become indented. At later stages many fibres were observed with both scanning and transmission electron microscopy to grow along the surface of the neural tube. These changes in neuroepithelial cell morphology and fibre pathway allow axons to form bundles which take a fairly straight course in contrast to the winding path which must be taken by the first axons to grow through the intercellular clefts.

Animals↗
PubMed1985

The relationship between altered blood vessel structure, hypertension, and the sympathetic nervous system.

The relationship between sympathetic innervation and arterial medial development has been examined in normotensive, hypertensive, and diabetic rats. Using the jejunal artery as a model, the number of nerve fibres innervating the artery as determined from fluorescent preparations, and the medial thickness and lumen diameter as measured from resin embedded specimens were correlated from animals prepared in various ways. The rats used were normal Sprague-Dawley (SD), SD with induced hypertension, SD with diabetes induced with streptozotocin, SD sympathectomized with 6-hydroxydopamine, spontaneously hypertensive rats (SHR), SHR treated with capsaicin to prevent hypertension development, Wistar Kyoto rats (WKY), and WKY treated with capsaicin. Examination of the jejunal arteries from these rats at 12 weeks of age following normal development, or 8 weeks of hypertension development, or 8 and 12 weeks of diabetes, showed that increased innervation occurred in the SHR under all conditions, and in the diabetic rats after 8 weeks of diabetes. Medial hypertrophy occurred in the SHR and in the SD hypertensive only. It is concluded that the special relationship which exists between the sympathetic innervation and arterial media in the SHR does not occur during hypertension development in the SD rat, nor is it necessary for normal medial development in the SD rat. The sympathetic innervation does appear to have a trophic influence on vascular smooth muscle of diabetic rats, at least in the early stages of the disease.

Animals↗
PubMed1985

An examination of the arterial media in transplanted arteries of spontaneously hypertensive (SHR) and normotensive Wistar Kyoto rats (WKY).

The hypothesis that arterial medial hypertrophy occurs in the SHR due to genetic factors inherent to the arterial wall, was examined in jejunal arteries cross transplanted between four-week-old SHR and WKY rats as a shunt between the femoral artery and vein. Four weeks after transplant, the arteries were removed and processed for embedding in resin and measurement of wall parameters by light microscopy. It was determined that irrespective of the origin of the transplanted artery, the wall thickness of transplants was higher in SHR hosts than in WKY hosts. Taken with results from other studies, this suggests that genetic factors inherent to the arterial wall are not the cause of arterial hypertrophy in the SHR.

Animals↗
PubMed1984

The development of two subnuclei of the nucleus tractus solitarius in spontaneously hypertensive rats.

Changes in relative metabolic requirements and neuronal densities in the nucleus commissuralis (NC) and nucleus medialis (NM) of the nucleus tractus solitarius were studied in spontaneously hypertensive rats (SHR) during development. The changes in relative metabolic requirements in the two subnuclei of SHR between 2 and 12 weeks of age were similar to those previously reported for normotensive WKY at the same ages. However, the relative metabolic activity in the NC of 2- and 4-week SHR was significantly higher than in normotensive rats. The differences in metabolic requirements of the NC could not be explained by differences in the neuronal densities of this subnucleus in young SHR and may reflect abnormalities in developmental or functional activities in the pre-hypertensive rat. Neuronal densities in the NC of 8- and 12-week SHR and in the NM of 4-, 8- and 12-week SHR were significantly higher than in WKY controls. Differences in the neuronal densities in the NC and NM of SHR may be explained by a smaller brain size characteristic of this strain, but differences in the NC of SHR suggest that the alterations may underlie or result from the cardiovascular abnormalities associated with the spontaneous hypertension of this strain.

Animals↗
PubMed1984

Multiple-locus heterozygosity and the physiological energetics of growth in the coot clam, Mulinia lateralis, from a natural population.

The relationship between individual energy budgets and multiple-locus heterozygosity at six polymorphic enzyme loci was examined in Mulinia lateralis. Energy budgets were determined by measuring growth rates, rates of oxygen consumption, ammonia excretion and clearance rates. Enzyme genotypes were determined using starch gel electrophoresis. Growth rate and net growth efficiency (the ratio of energy available for growth to total energy absorbed) increased with individual heterozygosity. The positive relationship between observed growth and multiple-locus heterozygosity was associated with a negative relationship between routine metabolic costs and increasing heterozygosity. Reduction in routine metabolic costs explained 60% of the observed increased growth of more heterozygous individuals. When routine metabolic costs were standardized for differences in feeding rates, these standard metabolic costs explained 97% of the differences in growth rate. Lower standard metabolic costs, associated with increasing heterozygosity, have been proposed as a physiological mechanism for the relationship between multiple-locus heterozygosity and growth rate that has been reported for a variety of organisms, ranging in diversity from aspens to humans. This study demonstrates that reduction of standard metabolic costs, at least in clams, accounts for virtually all of the differences in growth rate among individuals of differing heterozygosity.

Animals↗
PubMed1984

The postnatal development of blood vessels in the optic nerve of normotensive and hypertensive rats.

The blood vessels in the optic nerve of normotensive and hypertensive rats have been examined at 2, 4, 8 and 12 weeks of age. The pattern of development was found to be different in the two strains, with the number of blood vessels in the hypertensive rat optic nerve being lower at 2 weeks, but greater at 12 weeks than the normotensive rat. There appeared to be no correlation between vascularity and either myelination or changes in the fibre diameter spectrum at the ages studied. It is concluded that while the cause of the increased vascularity of the optic nerve in hypertensive rats is not known, it appears to be without effect in the structural development of the optic nerve.

Animals↗
PubMed1983

The correlation between the development of sympathetic innervation and the development of medial hypertrophy in jejunal arteries in normotensive and spontaneously hypertensive rats.

The catecholaminergic innervation of jejunal arteries was examined during development in normotensive and hypertensive rats. It was determined that a hyperinnervation of jejunal vessels in the hypertensive rats is present from 2 weeks of age onwards, before significant elevation of blood pressure and medial hypertrophy of jejunal arteries occurs. It is concluded that this hyperinnervation may be causally related to the medial hypertrophy in arteries of hypertensive animals.

Age Factors↗
PubMed1983

The postnatal metabolic development of the nucleus commissuralis and nucleus medialis of the nucleus tractus solitarius.

The ontogeny of the metabolic requirements in the nucleus commissuralis (NC) and nucleus medialis (NM) of the nucleus tractus solitarius was studied in the postnatal rat using the [3H]2-deoxy-D-glucose autoradiography technique. It was found that the metabolic requirements in the NC and NM are not constant between 2 and 12 weeks of age. A high level of metabolic activity at 2 and 8 weeks is contrasted by a lower level at 4 and 12 weeks. The apparent changes in metabolic requirements are not related to the changes in blood pressure of the rats or neuronal densities of the subnuclei which occur as the rats mature, or to exchange vessel densities of the subnuclei. Thus the higher energy requirements of the NC and NM at 2 and 8 weeks of age suggest that developmental and/or functional processes are more active at these stages.

Animals↗
PubMed1982

Factors involved in the control of RNA synthesis during regeneration of the optic nerve in the frog.

The incorporation of tritiated uridine into retinal ganglion cells was studied following intra- and extracranial section of the optic nerve in the frog. It was found that incorporation increased to above control levels by two days following extracranial section of the optic nerve and by two weeks following intracranial section and was maintained at an elevated level until the regenerating optic nerve reached the diencephalon, at which point the rate of incorporation fell back to control levels. It is suggested that the signal for turning off increased uridine incorporation lies in the diencephalon, and that functional reconnection is not the signal.

Animals↗
PubMed1982

Stool viruses in babies in Glasgow. 4. Further hospital studies.

The events occurring during the time in hospital of 24 babies were recorded in detail, particularly those related to bowel function. The babies were admitted to a general paediatric unit with various diagnoses a total of 27 times during a six month period. The purpose of the study was to fill gaps in the records of a previous study (Scott et al. 1979) and to try to relate excretion of viruses detectable by electron microscopy to disturbances of bowel function (diarrhoea and/or vomiting). The results showed that a variety of viruses were associated with gastroenteropathy, that virus excretion could occur without disease and that hospital acquisition of virus is not uncommon. Antiobiotic treatment did not appear to precipitate diarrhoea in this small number of babies.

Anti-Bacterial Agents↗
PubMed1981

A study of degeneration, scar formation and regeneration after section of the optic nerve in the frog, Rana pipiens.

Degeneration, scar formation and regeneration have been studied after section of the optic nerve in the frog. In the normal optic nerve two types of macroglial cell were identified: astrocytes and oligodendroglia. Degeneration after injury proceeded rapidly in comparison with mammals but did not lead to the production of a dense scar. Before much scarring had developed, regenerating axons penetrated the lesioned area.

Animals↗
PubMed1981

Stereological analysis of the tunica media of the aorta and renal artery during the development of hypertension in the spontaneously hypertensive rat.

The relationship between the arterial blood pressure and the composition of the tunica media in spontaneously hypertensive, Wistar-America and Wistar-Kyoto rats was examined. The systolic blood pressure of the spontaneously hypertensive rat, measured through an intra-arterial cannula, was significantly higher than that of the controls from 5 weeks and became hypertensive by 18 weeks of age. However, the content of the tunica media of the abdominal aortal and renal artery of the spontaneously hypertensive rats, as revealed by EM stereological analysis, and measurements of the thickness of the wall and diameter of the lumen, were not significantly different from the controls, at least up to the age of 18 weeks. The result of the present investigation suggests that the elevation of arterial blood pressure in the spontaneously hypertensive rat during the first 18 weeks of postnatal development is not a result of stereologically detectable changes in the composition of the tunica media of the abdominal aorta and renal artery.

Animals↗
PubMed1980

Maternal phenylketonuria: abnormal baby despite low phenylalanine diet during pregnancy.

During a screening programme of 10000 pregnant women by the Guthrie test, a previously unrecognised phenylketonuric woman was detected. A low phenylalanine diet introduced from the 16th week of gestation failed to prevent fetal abnormality and mental retardation. Maternal phenylketonuria requires earlier diagnosis than can be achieved at the initial antenatal clinic visit if its teratogenic effects are to be prevented.

Congenital Abnormalities↗
PubMed1980

Early events in stricture formation in the guinea pig urethra.

The early stages of urethal stricture formation have been examined by light and electron microscopy after injury of the anterior urethra in the guinea pig. It was found that initially an ulcerated surface formed which was subsequently covered by simple then stratified squamous epithelium. The tissue of the stricture contained elongated myofibroblasts and clumps of multinucleated giant cells. It is suggested that the myofibroblasts are responsible for the formation of the stricture and that the giant cells may be involved in continued collagen synthesis.

Animals↗
PubMed1979

Stool viruses in babies in Glasgow. 3. Community studies.

Twenty-seven babies from one deprived housing area in Glasgow were followed-up regularly, for periods varying between 2 months and 11 months (mean 7 months), in a prospective study of the viruses to be found in their stools by electron microscopy. Weekly stool specimens were collected in the home together with a history of the baby's health. Additional stool specimens were obtained, up to a maximum of one per day, during admissions to hospital. Over 500 specimens were obtained at home and another 320 in hospital. A wide variety of viruses (over 200 recognizates) were detected and it has been possible to plot their temporal relation to disease episodes. It became apparent that virus excretion was frequently unaccompanied by evidence of illness and it has not been possible to describe a typical illness syndrome associated with any of the morphological types of virus observed. The results suggest that, in one area of Glasgow at least, patterns of virus excretion in young babies are complex and will need further elucidation before the need for a vaccine to prevent infantile diarrhoea could be defined.

Diarrhea, Infantile↗
PubMed1976

An investigation into the hypothesis of shifting neuronal relationships during development.

The projection of ganglion cells from the centre of the eye to the tectum has been followed during development in Xenopus by an autoradiographic technique. By comparing the caudal limit of this projection with a fixed line of cells labelled with tritiated thymidine the projection has been shown to shift caudally during development. This indicates a less rigid form of neuronal specificity than has previously been accepted.

Animals↗
PubMed1975

The ultrastructure of human male urethral stricture.

Biopsy material was examined from 20 urethral strictures at the time of urethroplasty, using ultramicroscopic methods not hitherto applied to the study of the pathogenesis of stricture. Abundant smooth muscle and elastic tissue was found in the post-inflammatory strictures. The scar tissue from post-traumatic strictures merely showed dense collagen. An anatomical basis for the well known difference between the fibrous and the resilent stricture is demonstrated, and the role of smooth muscle in the development and behaviour of strictures is discussed.

Humans↗