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Biomedical subjects

J Stone

Publications and source records attributed to J Stone.

At least 19 recordsLinked to original sources
PubMed1992

Morbidity of failed labor in patients with prior cesarean section.

OBJECTIVE: The aim of our study was to determine whether the reported increased morbidity associated with failed attempted vaginal birth after cesarean section is attributable to the presence of a uterine scar alone or to labor preceding a cesarean section. STUDY DESIGN: Primiparous women (N = 237) who underwent repeat cesarean section after a failed trial of vaginal birth after cesarean section were retrospectively compared with 1582 nulliparous women who underwent a primary cesarean section after a failed trial of labor. RESULTS: There were no significant differences in maternal or neonatal morbidity between the two groups except for an increase in the prevalence of thin meconium in patients undergoing primary cesarean section. CONCLUSION: Our results suggest that the presence of a previous cesarean section scar does not increase the overall baseline morbidity associated with cesarean section after labor.

Adult↗
PubMed1992

Postural changes in femoral artery blood flow in normal subjects, patients with peripheral vascular occlusive disease and patients undergoing lumbar sympathectomy, measured by duplex ultrasound flowmetry.

Regulatory peripheral vasoconstriction occurs in response to lower limb dependency. In mildly ischaemic limbs these responses are retained but are lost in patients with rest pain. Previously used methods have inherent difficulties when applied during postural change. We studied orthostatic responses in 12 normal subjects (aged 22-74 years, median 52 years) and 16 patients (aged 21-83 years, median 48 years) with mild and severe peripheral vascular disease using a duplex ultrasound flowmeter. In the normal subjects the 60-s mean common femoral artery volume flow values (ml min-1 +/- S.D.) were 77 +/- 83; -78 +/- 116; -190 +/- 136 for elevation, dependency and standing respectively. For claudicants (n = 7) the values were 18 +/- 37; -112 +/- 123; -216 +/- 103, respectively. In rest pain patients (n = 9) the responses were reversed, being -252 +/- 124; 131 +/- 89 and 184 +/- 85. Significant differences were apparent between elevation, dependency and standing flows, in each of the three groups (all p less than 0.0001). The rest pain group displayed characteristically different responses compared with both normal subjects and claudicants, for each postural change (p less than 0.0001 in all cases). Investigation of the dependency response was undertaken in eight further patients with rest pain before and after lumbar chemical sympathectomy and a characteristic pre-sympathectomy response predicted the clinical outcome.

Aged↗
PubMed1992

Lack of evidence of efficacy of cohorting nursing personnel in a neonatal intensive care unit to prevent contact spread of bacteria: an experimental study.

Nurse cohorting was investigated in a modern neonatal intensive care unit (NICU). During 99 days bacterial infection and colonization rates were determined in 100 infants experimentally assigned cohort or noncohorted care. Colonizing isolate identity was determined by plasmid profile analyses and biotyping in weekly surveillance cultures. Between Days 2 and 7, 3 infections occurred in cohorted infants but none in noncohorted ones. No secondary spread of infection or definitive colonization cluster occurred. The first colonization rate, at any site, was 0.53/patient-week in the noncohorted and 0.3 to 0.4 in the cohorted units (P greater than 0.05). Colonization ratios with species other than usual skin bacteria in the respiratory tract and with species other than Escherichia coli in the rectum were lower for noncohorted infants. Effective infection control practices in a modern NICU, including alcohol hand antisepsis, should obviate a need for cohorting.

Bacterial Infections↗
PubMed1992

Vascular changes and their mechanisms in the feline model of retinopathy of prematurity.

This study documents changes to retinal vasculature during the feline form of retinopathy of prematurity (ROP). The authors describe the closure and obliteration of retinal vessels during exposure to high oxygen, the pattern and tempo of growth of proliferative vasculature, which, after the return of the animal to room air, extends from the optic disc in a spectacular "rosette" pattern, the formation of preretinal vascular growths, and an initial lack of barrier properties in the new vessels. Finally, the response of the vasculature to the relief of hypoxia is reported, including the gradual establishment of barrier properties in the intraretinal vessels, the partial normalization of the proliferative vessels, and the abnormalities that persist. It is suggested that the vascular changes occur in successive stages: closure and obliteration during hyperoxia, vasoproliferation induced by hypoxia, and normalization after the relief of hypoxia with distinct cellular mechanisms and stimuli. It is argued that the same stages can be seen in the human form of ROP; two possible stimuli for the fibroplasia that damages the retina in human ROP are discussed.

Animals↗
PubMed1992

Degeneration of astrocytes in feline retinopathy of prematurity causes failure of the blood-retinal barrier.

This study addresses the role of astrocytes in the genesis of retinopathy of prematurity, examined in the feline model of this condition. Evidence is presented that the hypoxia of retinopathy of prematurity, in addition to inducing vasoproliferation, damages the retina directly. Retinal neurons survive the hypoxia, but the astrocytes, which are involved in the formation of the glia limitans of the retinal vessels, degenerate. Astrocytes subsequently recolonize the retina after a delay that matches the period of leakiness of the proliferative vasculature (described in the companion article). Given the evidence from other studies that the barrier properties of vessels are induced by their glia limitans, the authors suggest that the initial lack of barrier properties in the new vasculature is caused by the degeneration of astrocytes and that the subsequent formation of those properties is induced by the astrocytes that recolonize the retina some days later. The observation that astrocytes are more sensitive to hypoxia than neurons, at least in developing tissue, was unexpected. The literature reporting on the damage caused to central nervous tissue by hypoxia is consistent in assessing neurons as more sensitive and glial changes as a reaction to neuronal damage. The sensitivity of astrocytes found in this study and earlier in vitro research suggests that degenerated astrocytes can be replaced and their structural and functional relationships reestablished.

Animals↗
PubMed1991

Structure of the macroglia of the retina: sharing and division of labour between astrocytes and Müller cells.

A detailed comparison is made between astrocytes and Müller cells of the cat's retina, with emphasis on their structural specialisations. Evidence is presented that astrocytes and Müller cells both contribute to the formation of the inner glia limitans of the retina, the glia limitans of vessels, and the glial sheaths of neurones. In particular, it was noted that both astrocytes and Müller cells wrap bundles of ganglion cells axons, that both contribute processes to the glial convergence on the initial segments and node-like structures of axons, and that both wrap the somas of neurones in the ganglion cell layer. Further, it was noted that adherent junctions form between astrocytes, between Müller cells, and between astrocytes and Müller cells, but not between these cells and neurones, or among neurones. These similarities suggest that astrocytes and Müller cells function interchangeably in many respects, and we suggest that they be regarded as variants of macroglia. Quantitative differences between astrocytes and Müller cells were noted in their ensheathment of neurones. In particular, the glial sheaths around the somas of ganglion cells are formed predominantly by Müller cells, and the glial processes attached to node-like specialisations of their axons are formed mainly by astrocytes. One qualitative difference was noted between the two cell classes. The gap junctions which form between astrocytes do not form between Müller cells or between cells of the two classes. From these differences, and previously established features of their shape, orientation, distribution and origin, a hypothesis is developed of the specialisation of macroglia represented by Müller cells.

Animals↗
PubMed1991

Factors determining the migration of astrocytes into the developing retina: migration does not depend on intact axons or patent vessels.

Astrocytes migrate into the cat retina from the optic nerve, beginning from embryonic day (E) 52. Once they have entered the retina they concentrate along major axon bundles and fail to enter regions of the retina with high densities of neurones, in particular the area centralis region of the ganglion cell layer. These nonuniformities appear as the astrocytes spread over the retina during development, and in this study we have examined factors that might control their spread. First we examined astrocytes in a retina in which the axon bundles had degenerated following an optic nerve lesion at birth. The area over which astrocytes had spread was normal, suggesting that their spread does not depend on the presence of intact axons. Second, we noted that, despite the degeneration of all ganglion cells following the nerve lesion, astrocytes still did not spread over the area centralis. Their spread is apparently not inhibited by concentrations of neurones. Third, we examined astrocytes in retinas of animals raised in an atmosphere containing 70-80% oxygen, which prevents the formation of retinal vessels. Again, the area over which the astrocytes had spread was normal, suggesting that their spread does not depend on the presence of patent blood vessels. These negative findings led us to compare the distribution of spindle cells (precursors of retinal vasculature) and astrocytes in the cat during development. The close correspondence in their topographical distribution and the earlier spread of the spindle cells lead us to suggest that spindle cells provide a basal lamina component that may guide the migration of astrocytes.

Animals↗
PubMed1991

Factors determining the morphology and distribution of astrocytes in the cat retina: a 'contact-spacing' model of astrocyte interaction.

The retina provides a valuable opportunity to examine the interaction of astrocytes with neurones and vasculature, in adult tissue and in vivo. We have studied astrocytes in cat retina to delineate the interactions that determine their morphology and distribution. Their morphology varied with their interaction with surrounding cells, from a classic stellate shape to an elongated bipolar form associated with axon bundles. Evidence is presented that the distribution of astrocytes across the retina is determined by their morphology and by a previously unrecognised interaction between astrocytes, which we term 'contact-spacing,' in which astrocytes maintain contact with their neighbours through their processes, but keep their somas apart. Evidence is also presented that astrocytes are not influenced in their distribution by surrounding neurones, and the influence of developmental mechanisms is identified. These observations are summarised in a contact-spacing model of astrocyte distribution, and four predictions of the model are tested. The concentration of astrocytes along axon bundles dispersed when the axons degenerate but not when vessels were prevented from forming. Further, when both axons and vessels were eliminated, the concentrations of astrocytes dispersed and they became stellate in form. Finally, in the retina of the rat, in which astrocytes show no affinity for axons, the distribution of astrocytes is essentially uniform. We suggest that the contact-spacing interaction among astrocytes provides the anatomical basis of a functional glial network extending across the retina and throughout the central nervous system.

Animals↗
PubMed1991

"Sunbursts" in the inner plexiform layer: a spectacular feature of Müller cells in the retina of the cat.

A previously unrecognised structure in the cat retina is described. Seen in Golgi-impregnated, wholemounted retinas, each such structure comprises processes radiating across the inner plexiform layer from a dense, vellate core. The processes are numerous, and largely unbranched, and give the impression of rays radiating from a point source; the structure is therefore termed a "sunburst." Evidence is presented from Golgi-impregnated retinas, and from retinas labelled with monoclonal antibodies to Müller cells, that the core of each sunburst is the inner process of a Müller cell. The sunbursts are numerous and overlap extensively, so that when neighbouring sunbursts are impregnated, they are seen to form a dense mat of processes extending across the IPL. It is suggested that each Müller cell forms a sunburst and that sunbursts form a major glial component of the neuropil of the inner plexiform layer.

Animals↗
PubMed1991

Contact spacing among astrocytes in the central nervous system: an hypothesis of their structural role.

Astrocytes are found throughout the central nervous system. They interact closely with surrounding structures, their processes contributing to the glia limitans of the neural tube, and to the glial investment of blood vessels, and of the somas, axons, and synaptic structures of neurones. This paper presents evidence that astrocytes in the central nervous system also interact with each other in a dual way, adhering to their neighbours via their processes, and repelling the somas of those neighbours. We suggest that this interaction, which has been termed contact spacing, distributes astrocytes through the central nervous system, and forms the basis of their structural role.

Animals↗
PubMed1991

4B2: a monoclonal antibody to ganglion and bipolar cells in the retina of the cat, generated by intrasplenic immunization.

Using tissue from the inner layers of the retina as the immunogen, we have prepared a monoclonal antibody which is selective for two classes of neuron in the cat retina. The antibody, termed 4B2, was generated by intrasplenic injection, demonstrating that neuron-specific antibodies can be elicited by this technique, which requires only micrograms of immunogen. The 4B2 binds to the somas, dendrites and axons of ganglion cells. Double labelling with 4B2 and with a retrograde tracer injected into the retino-recipient nuclei of the brain demonstrates that, of the cell classes in the ganglion cell layer, 4B2 labels only ganglion cells, and that, amongst ganglion cells, 4B2 is strongly selective for large (alpha-) and medium-sized (beta- and perhaps gamma-) cells. Double labelling with 4B2 and with markers for amacrine cells confirms tht 4B2 does not label amacrine cells. Double labelling with 4B2 and with anti-GFAP confirms that 4B2 does not label the macroglia of the retina. The 4B2 also labels bipolar cells, showing their somas, dendrites and axons. The axons of the labelled cells terminate in large boutons, in the innermost part of the inner plexiform layer and in the ganglion cell layer. This level of termination suggests that 4B2 labels rod bipolars, and perhaps a subgroup of cone bipolars. Double labelling with 4B2 and with markers for amacrine, horizontal and Müller cells indicates that other cell classes with somas in the inner nuclear layer remain unlabelled. In addition, we have examined the ontogeny of 4B2 labelling in the cat retina. The developmental sequence of labelling with 4B2 follows the sequence in which the cells are born, first ganglion and then bipolar cells.

Animals↗
PubMed1991

Effect of postural change on common femoral artery volume flow, measured by duplex ultrasound, in normal subjects and patients with peripheral vascular disease.

Regulatory peripheral vasoconstriction occurs in response to adoption of the erect posture. Mildly ischaemic limbs are thought to exhibit near normal responses, but patients with rest pain show increases in blood flow on limb dependency. Previous methods of limb blood flow quantification (xenon clearance and venous occlusion plethysmography) have inherent difficulties when applied in these situations. We studied orthostatic responses in 12 normal subjects (aged 22-74 years (median 52) and 16 patients (aged 21-83 (median 48) with mild and severe peripheral vascular disease, using a duplex flowmeter system. In the normal subjects changes in the 60s mean, common femoral artery volume flow values were as follows (ml min-1 (1 SD]: 77 (83), -78 (116) and -190 (136), for elevation, dependency, and standing respectively. For claudicants (n = 7) the values were 18 (37), -112 (123) and -216 (103) respectively. In rest pain patients (n = 9) the responses were reversed, being -252 (124), 131 (89) and 184 (85) respectively. Significant differences were apparent between elevation, dependency and standing flows in each of the three groups (P less than 0.0001). Normal subject and claudicant responses on elevation and dependency differed significantly (P less than 0.0001 and 0.03 respectively). On standing, the responses were similarly significantly different. The rest pain group displayed characteristically different responses compared with both normal subjects and claudicants for each postural change (P less than 0.0001 in all cases). Duplex ultrasound volume flowmetry is non-invasive and offers an excellent method of quantifying physiological changes.

Adult↗
PubMed1991

Death of Mozart.

Explore the source record for details and available documents.

Austria↗
PubMed1991

Overcoming denial and increasing the intention to use condoms through the induction of hypocrisy.

Feelings of hypocrisy were induced in college students to increase condom use. Hypocrisy was created by making subjects mindful of their past failure to use condoms and then having them persuade others about the importance of condoms for AIDS prevention. The induction of hypocrisy decreased denial and led to greater intent to improve condom use relative to the control conditions. The implications of these findings for AIDS prevention are discussed.

Adult↗
PubMed1990

Carrier detection for Sanfilippo A syndrome.

Leukocytes from 21 obligate carriers in 12 Sanfilippo A families and 49 normal controls were assayed for heparan sulphamidase (EC 3.10.1.1) at 55 degrees C. At this assay temperature the results show an absolute distinction between heterozygous carriers and the normal controls.

Clinical Enzyme Tests↗