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Biomedical subjects

N A O'Rourke

Publications and source records attributed to N A O'Rourke.

At least 19 recordsLinked to original sources
PubMed2001

The poor quality of information about laparoscopy on the World Wide Web as indexed by popular search engines.

BACKGROUND: This study was undertaken to determine the quality of information on the Internet regarding laparoscopy. METHODS: Four popular World Wide Web search engines were used with the key word "laparoscopy." Advertisements, patient- or physician-directed information, and controversial material were noted. RESULTS: A total of 14,030 Web pages were found, but only 104 were unique Web sites. The majority of the sites were duplicate pages, subpages within a main Web page, or dead links. Twenty-eight of the 104 pages had a medical product for sale, 26 were patient-directed, 23 were written by a physician or group of physicians, and six represented corporations. The remaining 21 were "miscellaneous." The 46 pages containing educational material were critically reviewed. At least one of the senior authors found that 32 of the pages contained controversial or misleading statements. All of the three senior authors (LKN, NAO, GAF) independently agreed that 17 of the 46 pages contained controversial information. CONCLUSION: The World Wide Web is not a reliable source for patient or physician information about laparoscopy. Authenticating medical information on the World Wide Web is a difficult task, and no government or surgical society has taken the lead in regulating what is presented as fact on the World Wide Web.

Abstracting and Indexing↗
PubMed1997

Postmitotic neurons migrate tangentially in the cortical ventricular zone.

Patterns of cell movement play a key role in the establishment of the brain's functional architecture during development. The migration of neuronal progenitor cells has been hypothesized to disperse clonally related cells among different areas of the developing cerebral cortex. To test this model, we explored the migratory patterns of cells in the proliferative zone of the intact cortex of the ferret. After focal injections of DiI, labeled cells migrated in all directions and over long distances within the ventricular and subventricular zones. These cells expressed the neuron-specific marker TuJ1 and did not incorporate BrdU after cumulative labeling. Our results reveal an extensive tangential dispersion of cortical cells mediated predominantly or exclusively by the non-radial migration of postmitotic neurons.

Animals↗
PubMed1995

Arteriovenous fistulae complicating orthopaedic procedures.

Arterial injuries in general and arteriovenous fistulae in particular are uncommon complications of orthopaedic procedures. We report the case of a 75 year old patient who suffered an arteriovenous fistula following bone graft insertion for an un-united tibial fracture. Aetiology diagnosis and management of these potentially serious injuries are reviewed.

Aged↗
PubMed1995

Tangential migration of neurons in the developing cerebral cortex.

The mammalian cerebral cortex is divided into functionally distinct areas. Although radial patterns of neuronal migration have been thought to be essential for patterning these areas, direct observation of migrating cells in cortical brain slices has revealed that cells follow both radial and nonradial pathways as they travel from their sites of origin in the ventricular zone out to their destinations in the cortical plate (O'Rourke, N.A., Dailey, M.E., Smith, S.J. and McConnell, S.K. (1992) Science 258, 299-302). These findings suggested that neurons may not be confined to radial migratory pathways in vivo. Here, we have examined the patterns of neuronal migration in the intact cortex. Analysis of the orientations of [3H]thymidine-labeled migrating cells suggests that nonradial migration is equally common in brain slices and the intact cortex and that it increases during neurogenesis. Additionally, cells appear to follow nonradial trajectories at all levels of the developing cerebral wall, suggesting that tangential migration may be more prevalent than previously suspected from the imaging studies. Immunostaining with neuron-specific antibodies revealed that many tangentially migrating cells are young neurons. These results suggest that tangential migration in the intact cortex plays a pivotal role in the tangential dispersion of clonally related cells revealed by retroviral lineage studies (Walsh, C. and Cepko, C. L. (1992) Science 255, 434-440). Finally, we examined possible substrata for nonradial migration in dorsal cortical regions where the majority of glia extend radially. Using confocal and electron microscopy, we found that nonradially oriented cells run perpendicular to glial processes and make glancing contacts with them along their leading processes. Thus, if nonradial cells utilize glia as a migratory substratum they must glide across one glial fiber to another. Examination of the relationships between migratory cells and axons revealed axonal contacts with both radial and nonradial cells. These results suggest that nonradial cells use strategies and substrata for migration that differ from those employed by radial cells.

Animals↗
PubMed1995

The valve design of disposable and reusable trocars.

The advent of video-laparoscopy has led to many recent improvements in the design of both disposable and reusable trocars and cannulae. This paper discusses the various types of trocar sheath valve mechanisms available to the laparoscopic surgeon. For reusable cannulae it is suggested that controllable flap valves are close to ideal, whilst for disposable cannulae controllable flap valves or silicone leaflet valves allow easy access and retrieval of instruments with minimal loss of pneumo-peritoneum.

Catheterization↗
PubMed1994

Rapid remodeling of retinal arbors in the tectum with and without blockade of synaptic transmission.

Dynamic rearrangements of axon terminal arbors may be critical for establishing appropriate connections in the developing nervous system. Here, the changes in complex retinal axon arbors in the tecta of live Xenopus larvae were followed during the formation of the topographic retinotectal projection. Three-dimensional reconstructions of terminal arbors made with a confocal microscope at hourly intervals revealed rapid remodeling of arbor extensions. Shorter branches were extended and retracted very rapidly, suggesting that they probe the environment for the optimal sites to form stable branches. About 27% of longer branches were present throughout the entire observation period and may be sites of stabilized synaptic contacts. Treatment of the animals to block postsynaptic activity resulted in increased rates of arbor rearrangements, which may coincide with decreased synapse stability. These studies reveal the dynamic behavior of nerve arbors and provide estimates for the lifetimes of retinotectal branches.

Animals↗
PubMed1993

Cell migration in cultured cerebral cortical slices.

In order to investigate the cellular mechanisms of migration and lamination in the mammalian cerebral cortex, we have cultured living slices of the developing telencephalon and tracked the migration of newly generated cortical neurons. Slice cultures made from neonatal ferret cortex were maintained in roller tubes and survived well for several weeks in vitro. Cells generated on Postnatal Day (P) 0 or 1 were labeled with the thymidine analog 5-bromo-2-deoxy-uridine (BrdU), and their movements were tracked during the subsequent culture period. At the beginning of the culture period, labeled cells were found almost exclusively in the proliferative zones of the cerebral wall, the ventricular and subventricular zones. Over the first week in culture, there was a dramatic movement of labeled cells out of the proliferative zones and into the cortical plate, the final destination of neocortical neurons. Comparison of the patterns of cell movement in cultured slices with that in intact littermate controls revealed that the initial migration of labeled cells into the cortical plate is similar in cultured slices and normal animals. The primary difference between migration in slice cultures and in vivo is that after longer times in culture, cells that migrate into the cortical plate fail to form the tightly clustered laminae characteristic of cells in the intact brain. Labeled cells are instead distributed more widely throughout the cortical plate and other regions of the cerebral wall. Thus, at least during the initial period of migration, cultured slices provide an experimentally manipulable system in which cell migration can be directly observed in a histotypically normal environment.

Animals↗
PubMed1993

The role of ERCP and endoscopic sphincterotomy in the era of laparoscopic cholecystectomy.

The advent of laparoscopic cholecystectomy (LC) has led to some controversy regarding the best method of managing bile duct calculi. This paper reviews the cases of 38 patients who underwent LC and endoscopic retrograde cholangiopancreatography (ERCP), from a series of 600 consecutive laparoscopic cholecystectomies. Twenty-nine patients had ERCP performed pre-operatively because of suspicion of choledocholithiasis. Duct stones were confirmed in eight patients. Recent or current jaundice was the best predictor of bile duct stones. Nine patients had ERCP done postoperatively because of duct stones seen on operative cholangiography. In two patients bile duct cannulation was not possible and a third procedure, open duct exploration, was necessary. Techniques in laparoscopic management of duct stones are improving and the role of ERCP and sphincterotomy should be limited to jaundiced patients or those with proven bile duct stones in whom laparoscopic procedures have been unsuccessful.

Adult↗
PubMed1993

Laparoscopic common bile duct exploration.

Twenty-one patients underwent laparoscopic common bile duct exploration during a 9 month period. Ten had stones flushed after ampullary dilatation. Seven had stones removed with a Dormier basket and one had direct common duct incision with T-tube insertion. Three failed attempted stone flushing and had stones removed by endoscopic retrograde cholangiopancreatography (ERCP) and sphincterotomy. Operating time ranged from 1.5 to 3.5 h. Nineteen patients were discharged by the second postoperative day. This early experience with laparoscopic stone removal is encouraging, reducing the need for pre-operative or postoperative ERCP.

Adult↗
PubMed1992

Diverse migratory pathways in the developing cerebral cortex.

During early development of the mammalian cerebral cortex, young neurons migrate outward from the site of their final mitosis in the ventricular zone into the cortical plate, where they form the adult cortex. Time-lapse confocal microscopy was used to observe directly the dynamic behaviors of migrating cells in living slices of developing cortex. The majority of cells migrated along a radial pathway, consistent with the view that cortical neurons migrate along radial glial fibers. A fraction of cells, however, turned within the intermediate zone and migrated orthogonal to the radial fibers. This orthogonal migration may contribute to the tangential dispersion of clonally related cortical neurons.

Animals↗
PubMed1992

Laparoscopic cholecystectomy for acute cholecystitis.

Sixty-eight cases of acute cholecystitis managed by laparoscopic cholecystectomy (LC) are reviewed. Thirty-two patients were admitted up to 10 days after onset of symptoms and 31 were completed by LC. One patient was referred from intensive care with gangrenous acalculus cholecystitis and was completed by LC but required subsequent laparotomy to control a bleeding omental vessel. Five patients were admitted with recurrent attacks of pain and histology confirmed resolving acute cholecystitis. Thirty patients had LC on routine operating lists, having recently had pain within 10 days of admission. Histology confirmed acute cholecystitis or resolving acute cholecystitis in these patients. All were completed by LC. Laparoscopic cholecystectomy is a very effective treatment for acute cholecystitis if complete dissection of anatomy can be performed.

Acute Disease↗
PubMed1990

Dynamic changes in optic fiber terminal arbors lead to retinotopic map formation: an in vivo confocal microscopic study.

Dynamic remodeling of retinal ganglion cell terminal arbors has been proposed to contribute to formation of the topographically ordered retinotectal projection. To test this directly, the growth of individual terminal arbors was observed in live X. laevis tadpoles using a confocal microscope to visualize their complex three-dimensional structure. During initial development, nasal and temporal retinal arbors covered overlapping tectal areas. Despite subsequent remodeling, the dimensions and positions of the temporal arbors remained relatively stable. In contrast, the nasal arbors grew caudally, as they extended caudal branches and retracted rostral branches. These results suggest that differences in the remodeling of the nasal and temporal arbors lead to the emergence of retino-topography along the rostrocaudal axis of the tectum. All the terminal arbors were dynamic, including those with stable dimensions, suggesting that continual remodeling of arbors may be a universal feature of neuronal projections.

Animals↗
PubMed1990

In situ analysis of neuronal dynamics and positional cues in the patterning of nerve connections.

Recently developed imaging techniques permit individual cells to be uniquely labeled and followed over time as development proceeds in intact vertebrate embryos. Small groups of cells in the developing eye rudiment of the frog Xenopus have been labeled with the vital dyes DiI, lysinated fluorescein dextran (LFD) or lysinated rhodamine dextran (LRD). Individual optic axons and their growth cones were clearly visible in the intact living animal using confocal microscopy or epifluorescence microscopy with a low light level video camera and computer-based video image enhancement. To follow the dynamics of single optic nerve fiber terminal arborizations, small groups of cells, or even single retinal ganglion cells, were labeled with DiI, and the resulting labeled optic nerve fibers were imaged using a confocal microscope. The images show a profound alteration in morphology from day to day, demonstrating that optic nerve terminal arborizations are dynamic structures constantly extending and retracting branches. To follow the topography of the developing projection and analyze the cues that guide its formation, small groups of eyebud cells from LFD- and LRD-labeled donor embryos were grafted to an unlabeled host in either a location equivalent to that from which they had been removed (homotopic grafts) or a non-equivalent location (heterotopic grafts). Axons from homotopic grafts projected to the tectum as expected from the adult topography of the retinotectal projection. Dorsoventral topography was present from the time that the optic nerve fibers were observable in the tectum, in agreement with previous work. Nasotemporal topography was subtle or absent for the first few days, and then slowly refined. The importance of positional cues was tested by performing heterotopic eyebud grafts, in which the labeled eyebud cells are grafted to inappropriate places in the host eyebud. The heterotopic grafts appeared to integrate with the ectopic site in the eyebud in a functional manner. They should, therefore, project to the tectum together with their new neighbors if neighbor interactions or activity-based cues were of primary importance in the initial patterning of the map. However, the experiments showed that the axons from heterotopic grafts always behaved in a fashion appropriate to their position of origin in the donor, regardless of their final position in the host. These observations indicate that small groups of eyebud cells (as small as a single cell) possess positional information that plays a dominant role in guiding the optic nerve fibers to their target sites in the tectum.

Animals↗
PubMed1989

Gradual appearance of a regulated retinotectal projection pattern in Xenopus laevis.

The topographic projection pattern formed by the retinal ganglion cell axons in the tectum of the lower vertebrate appears to require positional cues that guide the optic nerve fibers to their appropriate targets. One approach to understanding these positional cues or "positional information" has been to investigate changes in the pattern of the retinotectal projection after surgical manipulation of the embryonic eyebud. Analysis of these apparent changes in the patterns of positional information in the eye, termed "pattern regulation," may provide clues to both the nature of positional information and the mechanisms by which it is assigned to cells in the eyebud. Here we examine pattern regulation in the Xenopus visual system following the replacement of the temporal half of a right eyebud with the temporal half of a left eyebud. This manipulation requires that the left half-eyebud be inverted along its dorsoventral axis. Electrophysiological maps of these compound eyes in postmetamorphic frogs reveal regulated maps; the cells in the temporal half of the NrTl eye project to the tectum with a dorsoventral polarity appropriate for their position in the host eye and not appropriate for the original positions of the grafted cells in the donor eyebud. Paradoxically, the regulated patterns are not apparent in the projections of the original grafted eyebud cells during early larval development. Using fiber-tracing and electrophysiological mapping techniques, we now show that the regulated patterns appear gradually in the projections made by peripheral retinal cells added during mid-larval development. Because the regulation occurs relatively late in development and probably only in the peripheral retinal cells, simple models of epimorphic or morphallactic regulation do not appear to fit this system. Thus, new or more complex models must be invoked to explain the phenomenon of pattern regulation in the developing visual system of Xenopus.

Animals↗
PubMed1987

Head injuries to children riding bicycles.

This article examines the characteristics of 150 children who were admitted to Brisbane hospitals with head injuries that were caused by bicycle riding. These children constitute over 20% of all the children with head injuries who were admitted to hospital; accidents involving bicycle riding are the second largest single cause of head injury in these children, after falls. There was one death in the group, and three children were moderately disabled nine months after the injury. These four children all had Glasgow coma scores of less than 9 on their admission to hospital. Only two of the 150 children wore helmets. A survey of a random subgroup of children who had sustained head injuries confirmed our opinion that many children owned helmets but did not wear them for fear of peer derision. It is suggested that this refusal can be overcome by a combination of legislative enforcement, helmet design and promotion.

Australia↗
PubMed1986

Dynamic aspects of retinotectal map formation revealed by a vital-dye fiber-tracing technique.

In the visual system of Xenopus laevis, the axons from the retinal ganglion cells of the eye form a topographic projection onto the optic tectum. Many studies have focused on revealing the mechanisms responsible for this precise and regular projection pattern. In contrast to the static view of the system that one might expect from examining the regularity of the projection, recent work on its regeneration and its changes during larval development indicate that part of the patterning process involves the dynamic behavior of optic fibers. Typically, anatomical and electrophysiological techniques have been used to obtain static views of the developing retinotectal projection which then must be complied to provide a glimpse of any dynamic behavior. Here we report on experiments using a newly developed fiber tracing technique to directly follow the emergence of topography in the developing retinotectal projection. Defined halves of the developing eyebud were labeled with a vital fluorescent dye which fills the growing axons, and the projection of the labeled cells was followed for up to 2 weeks in individual animals. The experiments confirm that dorsal and ventral optic nerve fibers sort out into an ordered projection early in development. In contrast, nasal and temporal fibers initially overlap, and the same sets of prelabeled fibers then sort out into the adult topography over a period of days.

Animals↗