Biomedical subjects

L A Davis

Publications and source records attributed to L A Davis.

At least 37 records · Page 2Linked to original sources

PubMed1993

Incomplete neural deficits in thoracolumbar and lumbar spine fractures. Reliability of Frankel and Sunnybrook scales.

Because neural status is used both as a treatment determiner and outcome measure, a universal, reliable scale is required. Experienced personnel, provided with concise definitions, demonstrated high inter-rater reliability of Frankel and Sunnybrook scales (Pearson correlation coefficients 0.71-0.91), with 94-100% intra-rater agreement. Both scales correspond to total sensory and motor function but are insensitive to walking and bladder function. Frankel's wide clinical use, reliability, and simplicity identify it to be the preferred measurement system until a better alternative is developed. Discussion of neural status must include description of bladder and walking function.

Adolescent↗

PubMed1992

Antibodies to beta 1-integrins cause alterations of aortic vasculogenesis, in vivo.

Vasculogenesis is the de novo formation of blood vessels from mesoderm. This process occurs very early in development and provides a convenient system for studying morphogenesis in higher vertebrates. The cell-extracellular matrix (ECM) interactions that occur during dorsal aortic vasculogenesis were examined using the monoclonal antibody, CSAT, a reagent known to neutralize the ligand-binding activity of avian beta 1-integrins. We injected CSAT into quail embryos during a period of active vasculogenesis (4-10 somites). The CSAT antibodies, but not controls, had a marked and reproducible effect on aortic vessel formation. Vasculogenesis appeared to be arrested at the stage when slender cord-like assemblies of angioblasts rearrange to form tubules. Indeed, aortic primordia near the site of CSAT injection did not form patent vessels.

Animals↗

PubMed1992

Perturbation of beta 1 integrin-mediated adhesions results in altered somite cell shape and behavior.

Cell contact and adhesion between somites and the axial extracellular matrix (ECM) is likely to play a fundamental role in vertebrate development. In a preliminary report we showed that injection of the monoclonal antibody CSAT, which recognizes the avian beta 1 integrins, causes a lateral separation of both somites and segmental plate tissue from the embryonic axis (Drake and Little, 1991). In this study we addressed the cell biological response to CSAT injection, particularly the cell-ECM interactions involved in maintaining normal somite-axial relationships. A total of 150 stage 7-10 quail embryos have been injected with CSAT and then cultured for varying periods (1-30 hr). CSAT caused somitic cells to behave abnormally. Changes include, rounding-up, extensive blebbing, and formation of retraction fibers. A majority of separated somites were able to assume normal axial position with further time culture. Whether a somite subsequently aligned at the axis was dependent on the amount of CSAT injected and the postinjection culture period. Embryos in which somites remained separated from the axis after relatively long culture intervals (18-24 hr) displayed abnormal sclerotomal cell migrations. In no case did control injected embryos exhibit cellular alterations. Similarly, the injection of RGD-containing peptides had no detectable effect on somitogenesis or somite/segmental plate adhesion to the axis. On the basis of these data, we conclude that beta 1 integrins are necessary for normal somitic cell adhesions to the axis, but not somite segmentation and differentiation.

Amino Acid Sequence↗

PubMed1992

Clinical experience with reinforced, anchored intramuscular electrodes for functional neuromuscular stimulation.

Implanted intramuscular electrodes must remain functional for many years if functional neuromuscular stimulation (FNS) is to become a standard treatment in paralysed individuals. In initial trials we found that 5 of 11 coiled single-wire FNS electrodes implanted in 3 patients failed within 8 months. Consequently, we turned to a reinforced electrode comprising 2 multi-stranded, insulated wires tandem-wound on a prolene core and terminated by a prolene anchor or tine (after Mortimer et al., 1986, 1987). The electrodes were implanted with a translumbar aortogram needle, the teflon sheath of which enabled us to stimulate through the tip to guide placement. We have monitored the electrical and functional properties of 8 reinforced electrodes implanted in 2 incomplete quadriplegic patients over 22 months. Four of the electrodes were used for at least 1 h daily to exercise muscles or to provide FNS in gait. Electrical impedances, thresholds and elicited limb motion remained constant in all 8 electrodes over the test period. Disadvantages of the reinforced electrodes are (1) difficulty of eventual removal, and (2) risk of pathogenic infiltration is increased by the 3-filament structure (fortunately dense tissue encapsulation seems to mitigate infection). We conclude that tandem-wound, prolene-reinforced FNS electrodes are much more robust than previous single-coil designs and may form the basis for FNS devices of the future.

Adult↗

PubMed1992

A survey of vertebral burst-fracture management in Canada.

In the management of burst fractures, the role of direct surgical removal of retropulsed bony fragments encroaching upon the spinal canal (direct decompression) is controversial. A questionnaire was mailed to 65 neurosurgeons and 36 orthopedic surgeons across Canada to determine the current management of vertebral burst fractures and the willingness of these surgeons to participate in a longitudinal study of the effects of direct surgical decompression in the management of burst fractures. Sixty-nine (44 neurologic and 25 orthopedic) surgeons responded to the questionnaire. Of those who responded, 97% of the neurologic surgeons and 95% of the orthopedic surgeons stated that they used plain radiography and computed tomography in their pretreatment investigations, and at least 50% in each specialty repeated these investigations at follow-up examinations. Standard tomography, magnetic resonance imaging and myelography were used less frequently both before and after surgery. There were no significant differences between specialties in the use of tests. Neurologic status and the treating surgeon's specialty were found to significantly influence management of burst fractures. According to 56% of neurologic surgeons and 81% of orthopedic surgeons, neurologically intact patients were usually treated with stabilization only (p less than 0.05). The greater number of neurosurgeons who used direct decompression was balanced by the number of orthopedic surgeons who used indirect decompression. Patients with partial, stable neurologic injuries were usually managed by direct decompression and stabilization according to 84% of the responding neurologic surgeons and 77% of the responding orthopedic surgeons.(ABSTRACT TRUNCATED AT 250 WORDS)

Canada↗

PubMed1991

Spine trauma and associated injuries.

A longitudinal, prospectively gathered data base of spine trauma has been developed. A review of 508 consecutive hospital admissions identified the presence of associated injuries in 240 (47%) individuals, most frequently involving head (26%), chest (24%), or long bones (23%). Twenty-two per cent had one associated injury, 15% had two, and 10% had three or more. Most spine fractures involved the lower cervical (29%) or thoracolumbar junction (21%). Comparisons of presence or absence of associated injuries and spine fracture level showed significant differences (p less than 0.001). Eighty-two per cent of thoracic fractures and 72% of lumbar fractures had associated injuries compared to 28% of lower cervical spine fractures. While there was no significant relationship between type of associated injury and spine fracture level, those with associated injuries were less likely to have a neural deficit (p less than 0.05). After hospital admission, there were seven deaths. Early assessment and transport of spine trauma victims must be carried out with appropriate management of associated injuries. Conversely, multiple trauma victims must be handled with due regard for a possible spine fracture. The value of spinal units with specially trained personnel is emphasized.

Adult↗

PubMed1990

Avian vasculogenesis and the distribution of collagens I, IV, laminin, and fibronectin in the heart primordia.

The heart-forming regions of the early embryo are composed of splanchnic mesoderm, endoderm, and the associated ECM. The ECM of the heart-forming regions in stage 7-9 chicken embryos was examined using immunofluorescence. Affinity purified antibodies to chicken collagens type I and IV, chicken fibronectin, and mouse laminin were used as probes. We report that (1) the basement membrane of the endoderm contains immunoreactive laminin and collagen IV; (2) the nascent basement membrane of the heart splanchnic mesoderm contains immunoreactive laminin, but not type IV collagen, and (3) the prominent ECM between the splanchnic mesoderm and the endoderm (the primitive-heart ECM) contains collagen IV, collagen I, fibronectin, but not laminin. In addition, we describe microscopic observations on the spatial relationship of cardiogenic cells to the primitive-heart ECM and the endodermal basement membrane.

Animals↗

PubMed1989

Distribution of laminin, collagen type IV, collagen type I, and fibronectin in chicken cardiac jelly/basement membrane.

Light microscopic immunolabeling studies were designed to identify and locate structural components within the cell-free extracellular matrix which lies between the embryonic endocardial and myocardial tubes. Affinity-purified antibodies were used to examine stage 15-22 embryonic chicken hearts. Specimens were immunolabeled by using three different methodologies: 1) postembedding labeling of 10 microns cryostat sections, 2) preembedding labeling (en bloc) of whole hearts, and 3) postembedding labeling of ethanol/acetic acid-fixed paraffin sections. Our results establish the spatial distribution of collagen type I and demonstrate for the first time the presence of collagen type IV and laminin in the myocardial-basement-membrane/cardiac jelly.

Animals↗

PubMed1989

Embryonic heart mesenchymal cell migration in laminin.

Laminin, a large glycoprotein and major component of basement membranes, influences cell adhesion, migration, morphology, and differentiation. A peptide sequence, YIGSR, from the B1 chain of laminin has been found to correspond to an active site for cell adhesion. We report here that cardiac mesenchymal cells migrate vigorously within three-dimensional gels of laminin and that the YIGSR peptide will completely abolish this migratory activity. In contrast, migration of the mesenchymal cells into three-dimensional gels composed of collagen or collagen + laminin is not effected by YIGSR or other peptides (GRGDS, GRGDTP) reported to mediate cellular adhesion.

Animals↗

PubMed1988

Comparison of different methods for the purification of eosinophils from human peripheral blood.

Eosinophils are often purified in discontinuous gradients. Since continuous gradients usually provide a greater recovery of more highly purified cells, the present investigation was undertaken to compare the purification of eosinophils from normal whole blood in continuous and discontinuous gradients of Percoll. Contrary to our expectations, recovery and purity of eosinophils obtained from the discontinuous gradients were comparable to or higher than those from the continuous gradients of Percoll that were tested with whole blood. The purity of the modal fractions of eosinophils from the discontinuous gradients was between 88 and greater than 99% of the nucleated cells and from the continuous gradients, 80 to 93% of the nucleated cells. We have compared continuous and discontinuous gradients with many different kinds of cells. This is the first time we have found continuous and discontinuous gradients equally effective. We speculate this finding is related to the fact that the band capacities are vastly overloaded in these gradients. In addition, we tested the rate of superoxide production by eosinophils from the same donors after their purification by two different methods in discontinuous gradients. Eosinophils purified from normal whole blood in gradients of Percoll by a modification of the method of Roberts and Gallin [1985) Blood 65, 433-440) had a higher rate of superoxide production after stimulation with phorbol myristate acetate than those purified from leukocyte-rich plasma in gradients of Metrizamide by the method of Vadas et al. [1979) J. Immunol. 122, 1228-1236).

Cell Separation↗

PubMed1988

Replacing a chronic schizophrenic man's delusional speech with stimulus appropriate responses.

This study attempted to extend the use of Cues, Pause, Point language training procedures (developed to treat the speech disorders of mentally handicapped persons) to delusional speech. The direct and potential generalized effects of the procedures on the delusional and socially appropriate responding of an institutionalized, chronic schizophrenic man were evaluated in a multiple baseline design across stimulus-response pairs. The procedures encouraged the subject to (a) remain quiet before, during, and after the presentation of verbal stimuli and then (b) respond on the basis of environmental cues (i.e. written word cards) that contained the correct responses. Delusional responding was rapidly replaced by appropriate responding on both sets of the trained stimuli. Across person and setting generalization occurred in assessments conducted immediately following training, and these effects were maintained for 15 months. The results suggest that Cues, Pause, Point procedures may offer some potential for replacing delusional responding with appropriate responding to social stimuli.

Aged↗

PubMed1988

The nonoperative treatment of burst fractures of the thoracolumbar junction.

Treatment of thoracolumbar spine burst fracture with a neurologically intact patient is controversial, with advocates of operative and nonoperative approaches. Of 404 patients in a prospective spinal trauma study, 21 had burst fractures, were neurologically intact, and had greater than 1-year followup. This group was analyzed to evaluate treatment with early mobilization using a thoracolumbar total contact orthosis. The average time in a brace was 6 months. Two patients had pulmonary embolus treated successfully with anticoagulants. No patient required subsequent surgery for increasing kyphosis or neurologic deficit. Change in K angle at followup was 4.6 degrees (+/- 5.7) and change in anterior vertebral height was 6.1 degrees (+/- 10). All patients had a satisfactory pain score and most individuals returned to full employment. It is concluded that it is not necessary to routinely treat patients operatively with burst fractures if they fulfill the following criteria: 1) neurologically intact; 2) kyphosis angle less than 35 degrees; 3) other injuries do not preclude the use of a total contact orthosis; and 4) the patient is capable of understanding and cooperating with the treatment regime. These criteria are irrespective of the CT findings of posterior vertebral retropulsion and spinal canal narrowing.

Adolescent↗

PubMed1987

Induction of myofibrillogenesis in cardiac lethal mutant axolotl hearts rescued by RNA derived from normal endoderm.

A strain of axolotl, Ambystoma mexicanum, that carries the cardiac lethal or c gene presents an excellent model system in which to study inductive interactions during heart development. Embryos homozygous for gene c contain hearts that fail to beat and do not form sarcomeric myofibrils even though muscle proteins are present. Although they can survive for approximately three weeks, mutant embryos inevitably die due to lack of circulation. Embryonic axolotl hearts can be maintained easily in organ culture using only Holtfreter's solution as a culture medium. Mutant hearts can be induced to differentiate in vitro into functional cardiac muscle containing sarcomeric myofibrils by coculturing the mutant heart tube with anterior endoderm from a normal embryo. The induction of muscle differentiation can also be mediated through organ culture of mutant heart tubes in medium 'conditioned' by normal anterior endoderm. Ribonuclease was shown to abolish the ability of endoderm-conditioned medium to induce cardiac muscle differentiation. The addition of RNA extracted from normal early embryonic anterior endoderm to organ cultures of mutant hearts stimulated the differentiation of these tissues into contractile cardiac muscle containing well-organized sarcomeric myofibrils, while RNA extracted from early embryonic liver or neural tube did not induce either muscular contraction or myofibrillogenesis. Thus, RNA from anterior endoderm of normal embryos induces myofibrillogenesis and the development of contractile activity in mutant hearts, thereby correcting the genetic defect.

Ambystoma↗

PubMed1985

A possible physiological basis for the dud-stud phenomenon.

Intact male rats were tested on two successive weekly tests with females to determine their level of sexual activity. Nuclear estrogen receptor content was measured in specific brain regions of individual sexually responsive and sexually nonresponsive males. Sexually nonresponsive male rats had significantly reduced nuclear estrogen receptor levels in the preoptic area compared to sexually responsive males. Sexually active males did not differ from inactive males in nuclear estrogen receptors in the medialbasal hypothalamus.

Animals↗

PubMed1985

Immunoelectron microscopic localization of alpha-actinin on Lowicryl-embedded thin-sectioned tissues.

A procedure has been developed for the immunoelectron microscopic localization of intracellular antigens on thin-sectioned tissues. The tissues were fixed in a periodate-lysine-paraformaldehyde solution or a formaldehyde-glutaraldehyde combination and embedded in the acrylate-methacrylate mixture, Lowicryl K4M (Polaron), which was polymerized under ultraviolet irradiation at -35 degrees C. Thin sections were mounted on gold grids, immunostained using an indirect method with ferritin-labeled antibodies, and, optionally, counterstained with osmium tetroxide and/or lead citrate and uranyl acetate. The procedure provided good morphologic preservation of the cell architecture in adult and embryonic heart, and skeletal and smooth muscle tissue, as well as nonmuscle cells. At the same time it retained the antigenicities of several contractile proteins, including myosin, tropomyosin, actin, and alpha-actinin. The method has advantages over en bloc staining techniques in that the problem of antibody penetration into the cells is eliminated and careful controls can be performed on adjacent sections. This technique will be useful for localizing, at the ultrastructural level, contractile and other selected proteins in a variety of muscle and non-muscle cells. Details of the new protocol and a description of the results of using antibody against the contractile protein, alpha-actinin, are given.

Acrylic Resins↗

PubMed1984

Treatment of femoral fractures with the cast brace.

The authors report a retrospective review of 82 patients with femoral fractures treated nonoperatively by skeletal traction and cast bracing at the University of Alberta Hospital between 1975 and 1979. Fractures were classified as stable or unstable and the position of the fracture was assessed at the time of application of the cast brace and at the time of removal, using angulation, shortening and healing time as criteria for classification of results. Satisfactory results were seen in 88% of patients. At the time of cast brace removal, average knee flexion was 97 degrees, thigh atrophy was 2.5 cm and shortening was 1.4 cm. The unsatisfactory results are analysed and a protocol for successful use of the cast brace is suggested.

Adolescent↗

PubMed1981

Effects of vitamin A on endocardial cushion development in the mouse heart.

Retinoic acid (RA) (78mg/kg) administered to ICR mice on days 9.0,9.5 and 10.0 of pregnancy (plug day = day 1), resulted in cardiac malformations in 37.6% of the surviving fetuses, including transposition of the great arteries, ventricular septal defects, and double outlet right ventricle. Histological examination of the hearts of embryos observed 24 hours after in vivo or in vitro exposure to RA on day 9 revealed abnormalities in endocardial cushion tissue. The volume of the atrioventricular endocardial was reduced in treated embryos as was the ratio of the size of the cushions to the size of the heart. The endothelial layer of the atrioventricular endocardial cushions appeared to be unaffected by the retinoic acid, however, the mesenchymal cushion cells were significantly reduced in number when compared with controls. Labeling with [3H]-thymidine indicated that the mitotic activity of the mesenchymal cell population was significantly decreased while that of the endothelial cells was comparable to control levels. The extracellular matrix or cardiac jelly of the endocardial cushions also appeared to be affected by RA exposure, as shown by studies utilizing colloidal iron to stain GAGs, which revealed a decrease in the amount of stainable material in treated cushions. Two possible cause for the reduced thymidine index of the cushion mesenchyme are discussed, namely, a direct effect of RA on the mesenchymal cells or an indirect effect via the altered extracellular matrix of the cushion tissue.

Abnormalities, Drug-Induced↗

PubMed1980

Fractures and fracture-dislocations of the neck of the talus.

Forty fractures and fracture-dislocations of the neck of the talus are reviewed. Undisplaced fractures are associated with a high proportion of good results. Type II fractures, where there has been subluxation of the subtalar joint, require accurate reduction to avoid subtalar joint incongruity, and have a 20% incidence of avascular necrosis. Type III fractures, with dislocation of the body of the talus, have a poor prognosis and have a 100% incidence of avascular necrosis. Hawkins' sign of subcortical radiolucency is helpful in ascertaining the presence or absence of avascular necrosis. Accurate open reduction and rigid internal fixation with early range of motion of the involved joints is recommended where a closed reduction has failed to provide anatomic reduction.

Adolescent↗