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R Myers

Publications and source records attributed to R Myers.

177 records · Page 10Linked to original sources
PubMedDate not supplied

Area V5 of the human brain: evidence from a combined study using positron emission tomography and magnetic resonance imaging.

In pursuing our work on the organization of human visual cortex, we wanted to specify more accurately the position of the visual motion area (area V5) in relation to the sulcal and gyral pattern of the cerebral cortex. We also wanted to determine the intersubject variation of area V5 in terms of position and extent of blood flow change in it, in response to the same task. We therefore used positron emission tomography (PET) to determine the foci of relative cerebral blood flow increases produced when subjects viewed a moving checkerboard pattern, compared to viewing the same pattern when it was stationary. We coregistered the PET images from each subject with images of the same brain obtained by magnetic resonance imaging, thus relating the position of V5 in all 24 hemispheres examined to the individual gyral configuration of the same brains. This approach also enabled us to examine the extent to which results obtained by pooling the PET data from a small group of individuals (e.g., six), chosen at random, would be representative of a much larger sample in determining the mean location of V5 after transformation into Talairach coordinates. After stereotaxic transformation of each individual brain, we found that the position of area V5 can vary by as much as 27 mm in the left hemisphere and 18 mm in the right for the pixel with the highest significance for blood flow change. There is also an intersubject variability in blood flow change within it in response to the same visual task. V5 nevertheless bears a consistent relationship, within each brain, to the sulcal pattern of the occipital lobe. It is situated ventrolaterally, just posterior to the meeting point of the ascending limb of the inferior temporal sulcus and the lateral occipital sulcus. In position it corresponds almost precisely with Flechsig's Feld 16, one of the areas that he found to be myelinated at birth.

Adult↗
PubMedDate not supplied

Old and new concepts for the role of chi in bacterial recombination.

The DNA sequence 5'[GCTGGTGG]3', which is called chi, stimulates recombination that is mediated by the RecBCD pathway of Escherichia coli. In 1981, a model was proposed in which the RecBCD enzyme enters DNA at a double-chain end. The enzyme then travels between the chains by unwinding and rewinding the DNA at different rates so that the traveling enzyme becomes encumbered by a region of unwound DNA. Upon meeting chi, the enzyme was supposed to cut one of the two unwound chains, generating thereby a recombinagenic single-chain end. The model, based on microscopical observations of RecBCD enzyme interacting with linear duplex DNA, was supported by the subsequent finding that RecBCD acting in vitro under certain conditions did deliver a nick at chi. This widely embraced model has been challenged by a model in which the exonuclease activity of RecBCD destroys DNA from the enzyme's entry site to chi. The role of chi according to the new model is to inhibit this nuclease activity of RecBCD, perhaps by ejecting the RecD subunit from the enzyme, thereby revealing the enzyme's recombinase activity.

Base Sequence↗
PubMedDate not supplied

A national survey of dental protocols for the patient with a cardiac transplant.

To assess current practice of dental protocols for the patient with a cardiac transplant, a 19-question survey was designed and distributed to all general practice and oral surgery residency programs accredited by the American Dental Association. Analysis of the survey demonstrates a great amount of variability in the protocols used in this field. With the discovery of cyclosporine in 1976 by Borel, organ transplantation surgery has become increasingly common. This is especially true of heart transplantation. Success rates have increased dramatically in recent years; they are now documented at 81% at 1 year, 74% at 2 years, and 50% at 5 years. The two primary causes of death after cardiac transplantation are organ rejection and infection. Cyclosporine and azathioprine have improved the delicate balance between preventing organ rejection and encouraging infections. However, numerous bacterial infections, viral infections, and fungal infections may originate in the mouth and become life-threatening problems. For this reason, dentists must be members of the cardiac transplant teams and a nationally accepted dental protocol should be devised to ensure proper patient care.

Dental Care for Persons with Disabilities↗
PubMedDate not supplied

Changes in cochlear blood flow during acoustic stimulation as determined by 14C-iodoantipyrine autoradiography.

Local blood flow was measured in the tissues of the cochlea using the [14C]iodoantipyrine autoradiographic technique. Flow observed without acoustic stimulation was compared with that seen during exposure to wide-band noise at 85 or 105 dB SPL. Compared with the unexposed cochlea, substantial increases in blood flow were observed during exposure to 85 dB SPL noise in the spiral ganglion, VIII nerve and spiral lamina. Little or no change was noted in external wall structures. These results are consistent with changes in cochlear metabolism which have been reported previously using similar techniques, suggesting that increases in blood flow may be linked to increases in local metabolism. No changes in blood flow were measured during exposure to 105 dB SPL noise. This result is similar to those of other investigators using potentially damaging intensities of acoustic stimulation.

Acoustic Stimulation↗
PubMedDate not supplied

Acute and late damage in mouse tail following hyperthermia and X-irradiation.

Tissue injury following X-irradiation of adult mouse tail was assessed by: (a) the severity of the acute skin reaction, which appeared on day 13 and peaked at approximately 20 days after treatment; (b) the occurrence of necrosis by three months; and (c) the incidence of "late' necrosis which developed between 6.5 and 11 months after treatment, in tails whose gross appearance was normal at 3 months. Hyperthermia (44.0 or 44.5 degrees C for 30 min, by hot-water immersion) given 9 days after radiation, i.e. close to the time of appearance of the acute skin reaction, resulted in an increased thermal response and, in addition, an increase in tissue response for all three waves of radiation injury studied. The times of expression of injury remained unaltered and the degrees of thermal enhancement of both early and "late' necrosis were similar to that measured for the acute skin reaction following radiation. All values were significantly lower than the thermal enhancement ratio (TER), measured as a result of a primary interaction between heat and radiation when the two modalities are given in close association. The observed increase in "late' injury could be accounted for by thermal potentiation of the acute radiation response; there was no evidence for a significant exacerbation by a "late' or progressing thermal injury.

Analysis of Variance↗
PubMedDate not supplied

Extracorporeal whole body hyperthermia treatment of HIV patients, a feasibility study.

The literature supports that the retrovirus, Human Immunodeficiency Virus (HIV), which is thought to cause Acquired Immunodeficiency Syndrome (AIDS), is heat sensitive at temperatures which can be achieved in man. Invasive or non-invasive induction of whole body hyperthermia (WBH) has been used to treat an array of illnesses, primarily in the field of oncology, until recently. Non-invasive methods have proven to be less toxic than invasive means. However, new technology and refined patient management have shown a dramatic decrease in the side effects with extracorporeal whole body hyperthermia (EWBH). The Food and Drug Administration granted a prospective trial for six HIV positive/AIDS patients to undergo a single treatment of EWBH, with patients randomized to a core temperature of either 41 or 42 degrees C. All patients had failed antiretrovirals and experienced at least one episode of an opportunistic infection. Organetics, Ltd., PS-1 extracorporeal, centrifugal pump device was used to induce EWBH. Results of this feasibility study demonstrated the ability of this equipment and technique to induce EWBH with acceptable toxicity. It was not possible to assess efficacy in this small study.

Adult↗
PubMedDate not supplied

Salmonellosis in the Republic of Georgia: using molecular typing to identify the outbreak-causing strain.

In May 1998, three large outbreaks of salmonellosis, affecting 91 persons, were identified in the Republic of Georgia. Eighteen Salmonella Typhimurium strains were characterized by arbitrary primed polymerase chain reaction and pulsed-field gel electrophoresis; the results suggested that all cases were part of a single outbreak caused by a distinct clonal strain.

Disease Outbreaks↗
PubMedDate not supplied

Glutaraldehyde: an alternative to formocresol for vital pulp therapy.

Based on the limited results of this eight-week comparison of formocresol and glutaraldehyde, it would appear that glutaraldehyde may offer distinct advantages over formocresol, in the treatment of cariously exposed primary and young permanent teeth. In particular, due to its chemical structure, it is more active in fixing the surface tissues and is more rapidly limited in its depth of penetration through these tissues. Glutaraldehyde does not exhibit as significant an ability to induce the total loss of vitality, in the radicular pulp tissues. The progression of formocresol treated pulps to apparent fibrotic replacement via granulation-tissue ingrowth, through the apex, does not occur with the glutaraldehyde-treated pulp tissues. There may, however, be a slow progression of fibrotic replacement of the glutaraldehyde fixed tissue, in the coronal portion of the radicular pulp. Perhaps most importantly it would seem that since the glutaraldehyde does not perfuse the tissues to the apex, it will not demonstrate systemic distribution and other extradental phenomena, as have been identified with the use of formocresol

Aldehydes↗