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Biomedical subjects

P Bush

Publications and source records attributed to P Bush.

14 recordsLinked to original sources
PubMed1999

Anorganic bovine bone supports osteoblastic cell attachment and proliferation.

BACKGROUND: It was the aim of these studies to examine the ability of an anorganic bovine bone matrix material as an alternative to autogenous bone grafts and demineralized cadaver bone to support the attachment, spreading, and proliferation of isolated osteoblastic cells. METHODS: Primary culture osteoblastic cells were isolated from neonatal rat calvaria by sequential collagenase digestion. In the attachment studies, cells which had been labeled with 3H-leucine were incubated with the matrix material in sterile microfuge tubes for 15, 90, or 180 minutes or 24 hours. The attached cells were released and the radioactivity measured by liquid scintillation spectrometry. In the proliferation experiments, the cells were cultured with the matrix material for 24 hours and 3H-thymidine was added during the last 2 hours of the incubation. The cells were released and the radioactivity measured by liquid scintillation spectrometry. Scanning electron microscopy (SEM) was employed to observe osteoblastic cell interaction with the anorganic bone matrix. In these studies the cells were seeded on the bone graft material, then the material was removed and processed for SEM after 30, 60 or 120 minutes, or 24 or 48 hours. RESULTS: The cells attached to the matrix material in a time-dependent manner. There were significantly (P<0.05) more cells attached after 180 minutes than after the 15 and 90 minute incubations. The matrix material also supported proliferation of the attached osteoblastic cells. Cells seeded onto 100 mg of anorganic bovine bone resulted in significantly (P<0.05) more measurable proliferation than cells seeded onto 10 mg of material. The cells appeared to be round as they attached, then flatten and spread over time. There was also evidence of cellular processes extending into the pores of the material. CONCLUSIONS: These results demonstrate that this anorganic bovine bone graft material is able to support the attachment and proliferation of osteoblastic cells.

Animals↗
PubMed1998

Synthesis of large arrays of well-aligned carbon nanotubes on glass

Free-standing aligned carbon nanotubes have previously been grown above 700 degreesC on mesoporous silica embedded with iron nanoparticles. Here, carbon nanotubes aligned over areas up to several square centimeters were grown on nickel-coated glass below 666 degreesC by plasma-enhanced hot filament chemical vapor deposition. Acetylene gas was used as the carbon source and ammonia gas was used as a catalyst and dilution gas. Nanotubes with controllable diameters from 20 to 400 nanometers and lengths from 0. 1 to 50 micrometers were obtained. Using this method, large panels of aligned carbon nanotubes can be made under conditions that are suitable for device fabrication.

Journal Article↗
PubMed1998

GABAergic inhibitory control of the transient and sustained components of orientation selectivity in a model microcolumn in layer 4 of cat visual cortex.

Recently proposed models of orientation tuning in layer 4 of cat primary visual cortex (Somers, Nelson, & Sur, 1995; Douglas, Koch, Mahowald, Martin, & Suarez, 1995) rely on widespread inhibitory intracortical connections to suppress the nonoptimal component of a broadly tuned thalamic input, while local excitatory intracortical connections amplify the optimal component. However, new experimental data (Ferster, Chung, & Wheat, 1996) and theoretical analyses (Ferster, 1987; Krukowski, Priebe, & Miller, 1996) show that the temporally modulated component of thalamic input is well tuned and that the cortical circuitry must simply subtract an unmodulated DC component at nonoptimal orientations to obtain sharp tuning. In addition, within a single hypercolumn in layer 4, inhibitory and excitatory layer 4 neurons have approximately equal-sized axonal fields, making the most of their synapses within their own dendritic field (Kisvarday, Martin, Whitteridge, & Somogyi, 1985; Martin & Whitteridge, 1984). We have constructed a model of a single microcolumn in which GABA inhibition subtracts the DC and controls the sustained response, while GABA inhibition controls the response to transient and suprathreshold inputs. The model fits experimental data based on stimulation with drifting sine-wave gratings as well as flashed bars, explains a counterintuitive property of the GABA conductance, and at suboptimal orientations and submaximal contrasts produces an exponential distribution of firing frequencies.

Animals↗
PubMed1998

Endothelial dysfunction following thrombolysis in vitro.

OBJECTIVES: Thrombolytic therapy is frequently used to manage vascular graft thrombosis. However, long-term patency after thrombolysis remains poor. The purpose of this study was to characterise the morphological and functional response of endothelial cells (EC) exposed to a thrombus and subsequently lytic therapy. METHODS: Human EC were exposed to human whole blood thrombus for 2, 6, 12, and 24 h. The thrombus was lysed with urokinase. Cell morphology was studied with electron microscopy. Northern blot analyses were performed with human c-DNA probes for endothelin-1, thrombomodulin, tissue factor, tissue plasminogen activator, plasminogen activator inhibitor, and triose phosphate isomerase. RESULTS: EC retraction occurred for each period of incubation. Thrombomodulin expression was increased 2.2-fold at 6 h and 2.4-fold at 24 h. t-PA expression was depressed proportionally to the duration of thrombus exposure. PAI and TF expression transiently increased 1.5-fold at 2 h of exposure and returned to baseline at 6 h. Endothelin expression remained unchanged. CONCLUSIONS: Except for a transient increase in TF expression and reversal of the tPA/PAI ratio, EC exposed to thrombus do not appear to become actively procoagulant. The increase in TM expression may reflect enhanced thromboresistance. However, EC retraction may be responsible for an increase thrombogenicity of saphenous vein graft after thrombosis and Urokinase therapy.

Cells, Cultured↗
PubMed1996

Inhibition synchronizes sparsely connected cortical neurons within and between columns in realistic network models.

Networks of compartmental model neurons were used to investigate the biophysical basis of the synchronization observed between sparsely-connected neurons in neocortex. A model of a single column in layer 5 consisted of 100 model neurons: 80 pyramidal and 20 inhibitory. The pyramidal cells had conductances that caused intrinsic repetitive bursting at different frequencies when driven with the same input. When connected randomly with a connection density of 10%, a single model column displayed synchronous oscillatory action potentials in response to stationary, uncorrelated Poisson spike-train inputs. Synchrony required a high ratio of inhibitory to excitatory synaptic strength; the optimal ratio was 4 : 1, within the range observed in cortex. The synchrony was insensitive to variation in amplitudes of postsynaptic potentials and synaptic delay times, even when the mean synaptic delay times were varied over the range 1 to 7 ms. Synchrony was found to be sensitive to the strength of reciprocal inhibition between the inhibitory neurons in one column: Too weak or too strong reciprocal inhibition degraded intra-columnar synchrony. The only parameter that affected the oscillation frequency of the network was the strength of the external driving input which could shift the frequency between 35 to 60 Hz. The same results were obtained using a model column of 1000 neurons with a connection density of 5%, except that the oscillation became more regular. Synchronization between cortical columns was studied in a model consisting of two columns with 100 model neurons each. When connections were made with a density of 3% between the pyramidal cells of each column there was no inter-columnar synchrony and in some cases the columns oscillated 180 degrees out of phase with each other. Only when connections from the pyramidal cells in each column to the inhibitory cells in the other column were added was synchrony between the columns observed. This synchrony was established within one or two cycles of the oscillation and there was on average less than 1 ms phase difference between the two columns. Unlike the intra-columnar synchronization, the inter-columnar synchronization was found to be sensitive to the synaptic delay: A mean delay of greater than 5 ms virtually abolished synchronization between columns.

Cerebral Cortex↗
PubMed1988

Effect of age and day time on the adenosine modulation of basal and insulin-stimulated glucose transport in rat adipocytes.

1. The relationship between the activity of adenosine metabolizing enzymes 5'nucleotidase (5'N), adenosine kinase (A.K.) and adenosine deaminase (A.D.) with basal and insulin-stimulated glucose transport in isolated fat cells from young and old animals was studied at 08:00 and 16:00 hr. 2. In cells from young animals a larger insulin-stimulation of glucose transport was observed at 16:00 hr than at 08:00 hr. Also at 16:00 hr small changes in 5'N, A.K. and A.D. activities suggest a decrease in adenosine formation. 3. In the cells from old animals no effect of insulin was observed at any time, while a 3-5-fold increase in 5'N indicated a predominance of adenosine formation at both times studied. 4. An inverse relationship was observed in the changes of adenosine metabolism and insulin action.

Adenosine↗
PubMedDate not supplied

Significant enhancement of carbon dioxide removal by a new prototype IVOX.

The intravenacaval blood gas exchanger (IVOX) developed by Cardiopulmonics, Inc. has been tested in animals and in human clinical trials for partial support of gas exchange (25-30%) to allow reduction in mechanical ventilatory support and barotrauma during acute respiratory failure. After recognizing the limitations of the device and limited clinical utility of removing only 25-30% of CO2 production, the authors have made design changes in the IVOX (prototypes IIA and IIB), including increased fiber number, decreased fiber length, decreased fiber diameter, and increased crimping. Nine ewes underwent placement of the IVOX prototypes in an ovine model of severe smoke inhalation injury. A modification of the original insertion technique was used to implant the prototypes. CO2 removal was directly measured from the outlet gas. O2 exchange was calculated from IVOX on/off measurements. Neither IVOX IIA nor IIB significantly changed hemodynamics when a fluid bolus (15 ml/kg) was infused before insertion. There were no significant differences between prototypes regarding thrombosis, emboli, or incidence of bleeding complications. Both prototypes significantly improved CO2 removal (60-80%) compared with that reported for an older IVOX model. The improved gas transfer by these prototypes would serve to decrease mechanical ventilatory requirements and barotrauma in the treatment of severe respiratory failure.

Animals↗