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Biomedical subjects

J Cooke

Publications and source records attributed to J Cooke.

At least 19 recordsLinked to original sources
PubMed1992

The influence of an academic representative on prescribing by general practitioners.

1. The effect of providing information about medicines by a short 'sales' interview between individual general practitioners and an 'academic representative' on prescribing was investigated. 2. The promotional campaign was designed to encourage a rational approach to prescribing of non-steroidal anti-inflammatory agents in an intervention group of 101 general practitioners selected at random from the Leeds Family Practitioner Committee (FPC). The remaining general practitioners in the Leeds FPC acted as a reference group. 3. The prescribing data for each group for 5 months immediately prior to and 5 months following intervention were compared. 4. Intervention produced a significant increase (P less than 0.005) in the prescribing cost of ibuprofen, the non-steroidal promoted as first choice agent, which was sustained for at least 5 months. 5. Prescribing of the second choice agent, piroxicam, decreased in the reference group but not in the intervention group. 6. There was a decrease in the average prescribing cost of pounds 6.60 per doctor per month in the intervention group compared with the reference group.

Costs and Cost Analysis↗
PubMed1991

Effects of the steel gene product on mouse primordial germ cells in culture.

Mutations at the steel (sl) and dominant white spotting (W) loci in the mouse affect primordial germ cells (PGC), melanoblasts and haemopoietic stem cells. The W gene encodes a cell-surface receptor of the tyrosine kinase family, the proto-oncogene c-kit. In situ analysis has shown c-kit messenger RNA expression in PGC in the early genital ridges. The Sl gene encodes the ligand for this receptor, a peptide growth factor, called here stem cell factor (SCF). SCF mRNA is expressed in many regions of the early mouse embryo, including the areas of migration of these cell types. It is important now to identify the role of the Sl-W interaction in the development of these migratory embryonic stem cell populations. Using an in vitro assay system, we show that SCF increases both the overall numbers and colony sizes of migratory PGC isolated from wild-type mouse embryos, and cultured on irradiated feeder layers of STO cells (a mouse embryonic fibroblast line). In the absence of feeder cells, SCF causes a large increase in the initial survival and apparent motility of PGC in culture. But labelling with bromodeoxyuridine shows that SCF is not, by itself, a mitogen for PGC. SCF does not exert a chemotropic effect on PGC in in vitro assays. These results suggest that SCF in vivo is an essential requirement for PGC survival. This demonstrates the control of the early germ-line population by a specific trophic factor.

Animals↗
PubMed1979

Patients' reactions to a two-way mirror in general practice.

From a survey of 200 patients in two general practices it would appear that the patients' reaction to the use of a two-way mirror is on the whole not unfavourable. The results suggest, however, that in the very personal setting expected of general practice people suffering from psychiatric problems (especially depression) should be given every opportunity to decline consultation in front of the mirror and if any patient becomes upset, then the mirror should be 'turned off' immediately. Internal examinations should not take place when the mirror is in use.

Attitude↗
PubMed1979

Cell number in relation to primary pattern formation in the embryo of Xenopus laevis. I. The cell cycle during new pattern formation in response to implanted organizers.

Results are presented which offer strong evidence that extensive alteration of the fates of embryonic Xenopus cells occurs independently of the schedule of cell division, after operations which lead to a doubling of the axial pattern of mesodermal differentiation in the gastrula. The experimental strategy was to make estimates of total mesodermal cell numbers and mitotic index in closely matched sets, each of three synchronous sibling embryos, fixed during the ten hours following the close of gastrulation. Within each set two embryos, an unoperated control and a sham-operated embryo whose own dorsal-lip (organizer) cells had been replaced with an equivalent graft, were developing normally. The third, experimental embryo had received an organizer implant to replace an equivalent number of cells from its ventral marginal zone, and was thus developing two axial mesodermal patterns of differentiation in relation to two dorsal midlines, the extra pattern embracing much host tissue. Mitotic index was also determined, in specific regions and throughout the mesoderm, in similar sets of embryos but at mid-gastrula stages. The conclusions are justified by the results of a control investigation which show that there is normally no difference in cell cycle time along the presumptive dorso-ventral mesodermal, dimension, during the interval between time of operations and the determination of pattern. The lack of any enhancement of mesodermal cell number in late embryos with dual axia patterns, or intervening enhancement of mitotic index in younger operated embryos, thus suggests that new patterns may be determined in the Xenopus gastrula without generation of extra cells. The results are discussed in relation to recent ideas about pattern formation, and the concepts of morphallaxis and epimorphosis.

Animals↗
PubMed1979

Cell number in relation to primary pattern formation in the embryo of Xenopus laevis. II. Sequential cell recruitment, and control of the cell cycle, during mesoderm formation.

Morphological evidence is presented that definitive mesoderm formation in Xenopus is best understood as extending to the end of the neurula phase of development. A process of recruitment of cells from the deep neurectoderm layers into mesodermal position and behaviour, strictly comparable with that already agreed to occur around the internal blastoporal 'lip' during gastrula stage 20 (earliest tail bud). Spatial patterns of incidence of mitosis are described for the fifteen hours of development between the late gastrula and stage 20--22. These are related to the onset of new cell behaviours and overt cyto-differentiations characterizing the dorsal axial pattern, which occur in cranio-caudal and then medio-lateral spatial sequence as development proceeds. A relatively abrupt cessation of mitosis, among hitherto asynchronously cycling cells, precedes the other changes at each level in the presumptive axial pattern. The widespread incidence of cells still in DNA synthesis, anterior to the last mitoses in the posterior-to-anterior developmental sequence of axial tissue, strongly suggests that cells of notochord and somites in their prolonged, non-cycling phase are G2-arrested, and thus tetraploid. This is discussed in relation to what is known of cell-cycle control in other situations. Best estimates for cell-cycle time in the still-dividing, posterior mesoderm of the neurula lie between 10 and 15 h. The supposition of continuing recruitment from neurectoderm can resolve an apparent discrepancy whereby total mesodermal cell number nevertheless contrives to double over a period of approximately 12 h during neurulation when most of the cells are leaving the cycle. Because of pre-existing evidence that cells maintain their relative positions (despite distortion) during the movements that form the mesodermal mantle, the patterns presented in this paper can be understood in two ways: as a temporal sequence of developmental events undergone by individual, posteriorly recruited cells as they achieve their final positions in the body pattern, or alternatively as a succession of wavefronts with respect to changes of cell state, passing obliquely across the presumptive body pattern in antero-posterior direction. These concepts are discussed briefly in relation to recent ideas about pattern formation in growing systems.

Animals↗
PubMed1979

The orientation of the visuotectal map in Xenopus: developmental aspects.

Rotations and translocations of the eye anlage were performed in Xenopus embryos of stages ranging from 21/22 to 30. Some of the operations involved grafting wild-type eye anlagen into albino host orbits. Operations were performed under a variety of operating media and conditions. In later larval life, or after metamorphosis, the visuotectal maps from the operated eyes were recorded electrophysiologically. Results fell into two classes. In the majority, the orientation of the visuotopic map corresponded to the orientation of the eye at the time of recording. In the minority the visuotopic maps were 'compound', consisting of two parts each with its own independent orientation. The organization of the compound maps was such that one component was oriented in correspondence with the orientation of the eye, while the other component was normally oriented. Histological analysis and observations on genetically marked grafts indicated that the component parts of the compound eye were of dual cellular origin. The component giving the rotated (or translocated) map belonged to the originally operated eye tissue; whereas the component giving the normally oriented map was derived from newly grown eye tissue coming from the optic stalk. In no case was a normally oriented map obtained from a rotated or translocated eye. The results are discussed in relation to mechanisms proposed to account for the determination of map-related retinal specificity.

Animals↗
PubMed1978

Somite abnormalities caused by short heat shocks to pre-neurula stages of Xenopus laevis.

This paper describes the small disturbances, in the regular pattern of the somites and the fissures between them, that are seen following short (around 300 s) heat shocks at 37.5 degrees C delivered to pre-neurula stages of Xenopus laevis. Affected groups of cells still finally differentiate as somite muscle, but the normally precise spatio-temporal sequence in which they move beforehand to give rise to the actual pattern of somite blocks, is disrupted. Examination of the position and sizes of patches of disrupted morphogenesis, in relation to the precise embryonic stage at shock, leads to certain conclusions about the nature of the disturbance induced by a brief period at high temperature, in cells due to form somites. The pattern of results is compared with that produced by similar temperature shocks given to tail-bud (later) staged embryos. The discussion includes a brief consideration of how the various results of heat shocks, given at different embryonic stages, might be understood in terms of one particular model (Cooke & Zeeman, 1976) for the spatio-temporal control of the developing somite pattern.

Animals↗