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J Overton

Publications and source records attributed to J Overton.

At least 37 records · Page 2Linked to original sources
PubMed1984

Intra-operative spinal cord monitoring during surgery for scoliosis using somatosensory evoked potentials.

The method of intra-operative monitoring of spinal cord function by spinal somatosensory evoked potentials (SEP), as used at the Royal Alexandra Hospital for Children during surgery for scoliosis is described. Using a non-polarisable platinum spinal epidural electrode, SEP elicited by tibial and peroneal nerve stimulation in the popliteal fossa are recorded proximal to the level of spinal correction. The large amplitude and discrete waveform of the SEP enable rapid signal acquisition and easy interpretation. The spinal SEP is stable under both therapeutic hypotension and general anaesthesia. Electrophysiological monitoring has now superceded the 'wake-up' test as an index of spinal cord function during corrective surgery for scoliosis.

Adolescent↗
PubMed1984

The airway of patients with a lipid storage disease.

There have been no previous reports in the anaesthetic literature regarding the airway management during anaesthesia of patients with a lipid storage disease. In a 40-year period (1942-1982) at a busy paediatric hospital 15 patients with a lipid storage disease were anaesthetised on 19 occasions. Eight patients were intubated, three of them twice. No difficulties in airway management during anaesthesia were documented.

Adolescent↗
PubMed1983

Changes in intercellular junctions. I. Embryonic chick liver development.

Quantitation of junctional changes during development may clarify the relation between intercellular junctions and processes such as cell proliferation, morphogenesis, and cytodifferentiation. Chick embryo hepatocytes at 3 days (stage 21) 6 days (stage 28), 14 days (stage 39) of incubation, and 5 days posthatching showed thymidine-labeling indices of 41 +/- 1, 33 +/- 0.8, 13 +/- 0.04, and 7 +/- 1%, respectively. This decline in mitotic activity was correlated with a gradual increase in amount of cell surface occupied by tight junctions. In early embryonic stages these junctions were characteristically linear or macular in form. At embryonic stages 28 and 39 the anastomosing strands of the tight-junction networks characteristically had many free ends while in liver from hatched chicks, tight junction strands frequently ran almost parallel to one another. The area covered by gap junctions increased at embryonic stage 28, then declined with further development. Scanning electron microscopy of developing chick liver showed that the elongated cells of hepatic buds are reorganized into hepatic cords between embryonic stages 21 and 28. Cytochemical demonstration of ATPase at the bile canalicular surface is first apparent at embryonic stage 28 and the cell surface occupied by gap junctions is highest near this time. These findings suggest that modification of proliferative rate or of synthetic activity associated with the maturation of hepatocytes could be correlated with predictable changes in junctional patterns.

Animals↗
PubMed1983

Changes in intercellular junctions. II. Modulation in embryonic chick liver in vitro by cytosine arabinoside and dexamethasone.

We have used an in vitro model to investigate the relationship between cell proliferation, cell maturation, and intercellular junctional changes that are seen during normal liver development. Chick liver fragments of embryonic stages 21, 28, and 39 were grown in organ culture in Medium 199 with 10% bovine serum albumin for 24 hr. Concurrent cultures were treated with cytosine arabinoside (ara-c, 20 micrograms/ml) to inhibit cell proliferation or with dexamethasone (2 microns/ml) to promote cell maturation. Control and treated liver cultures were analyzed using autoradiography to determine labeling index and quantitative computer graphic analysis of freeze-fracture micrographs to evaluate junctional changes. Explants treated with ara-c had a near zero labeling index. Those from embryonic stage 21 showed a 4-fold increase in tight junctional area, while those from embryonic stage 28 showed a 2.5-fold increase in tight junctional area and a 5-fold increase in gap junctional area. In liver of embryonic stage 39, junctional area increased, and conformation of junctions took on the typical form seen in the liver of the hatched chick. Thus high mitotic activity appears to disrupt cell junctions, reducing the amount of junctions present and causing pleomorphic configurations. Junctional area could also be modified with no change in mitotic activity by treatment with dexamethasone. Stage 28 embryo livers in culture with dexamethasone showed a 4-fold increase in the amount of tight junctions with no change in the amount of gap junctions. Some major findings based on these age-dependent responses are (1) if mitosis is blocked in young embryonic stages when proliferation is high, intercellular junctions tend to increase in amount, and to be more mature in configuration; (2) if maturation is stimulated with no change in proliferation, those junctions which normally increase with differentiation will increase in amount; and (3) it is possible to produce a change in the amount of one junctional type without affecting the other. Therefore the amount of cell surface occupied by junctions at any given time seems to depend on both the pattern of synthetic activity in the cell and the degree to which cell to cell contacts are stable and undisrupted by mitotic activity.

Animals↗
PubMed1981

Epithelial cell-cell and cell substrate contacts.

An epithelial sheet maintains its normal morphology by an appropriate balance between cell to cell and cell to substrate contacts which must be adjusted as proliferation occurs. We review our studies which attempts to analyze some of these problems by recombining cell and matrix tissue components, or by analyzing developmental changes in intact tissue. Epithelial and mesenchymal cells placed on tissue matrices which have been denuded of their normal tissue components behave distinctively, suggesting that this procedure could reveal inherent differences. When chick epiblast is grown on the outer surface of the vitelline membrane, the mode of expansion changes from that seen in the normal site, the vitelline membrane inner surface. Dispersed skin and corneal cells studied during subsequent aggregation show that one cell can influence desmosome formation in another. Finally, recent studies on developing chick liver indicate a correlation between the percent of lateral cell surface in the junctional domain and the proliferative rate of these cells.

Animals↗
PubMed1979

Inhibition of desmosome formation in chick cell aggregates.

Desmosomes (macula adherens) have been associated with the function of adhesion. Their possible role in aggregation and sorting of chick and mouse epithelial cells has been investigated. Treatment of aggregates with 2-5 microgram/ml of actinomycin D which inhibited RNA synthesis also inhibited both desmosome formation and aggregation if administered at the beginning of the aggregation process. In contrast, if the drug was administered at six hours, when the cells had recovered from the process of dissociation, then aggregation over the following six hours appeared normal from observation of living samples. Such aggregates incorporated leucine-3H at roughly 85% of the control level. A quantitative comparison was made of desmosome formation in aggregates treated with actinomycin D for hours 6-12 and those cultured in normal medium. Desmosome formation was inhibited by the drug, although aggregation could proceed. Combinations of chick corneal and mouse skin cells sorted out in the presence of actinomycin D to the same extent as controls. Thus desmosome formation, which normally occurs during aggregation of the epithelial cells studied here, is not coupled with the aggregation or cell sorting process in these cells of stratified epithelia. When cells were treated with cycloheximide (100 muM) both desmosome formation and the progressive rounding up of aggregates was inhibited.

Animals↗
PubMed1979

Differential response of embryonic cells to culture on tissue matrices.

Cell responses to different natural substrates have been followed by scanning microscopy in order to evaluate the role of these substrates in morphogenesis. Matrix has been isolated then repopulated with suspensions of embryonic cells from chick skin, spinal ganglia, duodenal epithelium and heart. In some cases outgrowth from amphibian embryonic tissue was used. Basal lamina of the Xenopus tail may be exposed by freezing and thawing the tissue, or by EDTA treatment. The underlying lamella of orthogonally oriented collagen fibers may be exposed by use of trypsin or hyaluronidase. Trypsin causes more clumping of collagen fibers and a coarser texture of the matrix. On trypsin isolated basement lamella, nerve cell processes grow out on the surface and show no strong tendency to penetrate the lamella while skin mesenchymal cells commonly burrow among the collagen plies. Epithelial cells remain on the surface. On the basal lamina mesenchymal cells ruffle in early stages of culture, then flatten. Epithelial cells flatten rapidly on the lamina. These differences in cell response are in some cases closely related to cell behavior in vivo and suggest that cells show a selective response to the chemical composition of the substrate as well as to its physical conformation.

Animals↗
PubMed1977

Evacuation of retained products of conception in a treatment room and without general anaesthesia.

One hundred patients with an incomplete aboriton, 14 patients with retained products of conception after a second trimester termination, 5 patients with missed abortion and 2 patients with secondary postpartum haemorrhages (making a total of 121 patients) had a uterine evacuation in a treatment room using the portable Karman curette equipment. No general anaesthesia was used but patients were given intravenous pethidine or papavaretum (Omnopon) and diazepam. Four patients found the procedure painful but only two of them would have preferred general anaesthesia. There were no immediate complications but three patients required re-evacuation of the uterus.

Abortion, Incomplete↗