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Biomedical subjects

R E Snyder

Publications and source records attributed to R E Snyder.

At least 19 recordsLinked to original sources
PubMed1992

Changes in the linear attenuation coefficient of canine appendicular bone following intravenous infusion of strontium lactate, measured using gamma-ray computed tomography.

Changes in the average linear attenuation coefficient (LAC) within a fixed measurement volume in the proximal end of the dog tibia, which contains trabecular bone and associated soft tissues (the trabecular bone "space"), were monitored continuously using gamma-ray computed tomography (gamma-CT) prior to, during, and following intravenous infusion of strontium (Sr) lactate. An infusion of 1.3-4.7 g of Sr over a period of 110-160 minutes into 20-kg dogs resulted, within 6-8 hours, in an increase of 0.019-0.045 cm-1 (P less than 0.002) in the LAC. Calibration of the gamma-CT system showed that 0.44 mg/cm3 of Sr produced a change of 0.01 cm-1 in the LAC. Using this conversion factor, the Sr concentration in the trabecular bone space resulting from infusion, as measured by flame atomic absorption spectroscopy, agreed with that predicted by the change observed in the LAC. Sr present in the serum and urine was consistent with the changes observed in the LAC over the study period. Control dogs infused with mineral-free solutions showed no change in LAC. Calcium equivalents required to give the changes observed in the LAC using Sr indicate that variations in skeletal turnover in man can be monitored in the peripheral skeleton using gamma-CT.

Animals↗
PubMed1991

Reversal of rapid axonal transport at a lesion: leupeptin inhibits reversed protein transport, but does not inhibit reversed organelle transport.

The hypothesis that the reversal of rapid axonal transport requires a proteolytic conversion of anterograde transport vesicles was examined using sciatic nerve preparations from Xenopus laevis and leupeptin as an inhibitor of proteolysis. The transport of newly synthesized 35S-labeled proteins was studied with a position-sensitive detector of radiation. Organelle transport in isolated myelinated axons was studied by video microscopy. Leupeptin (0.1-0.4 mM) reduced the anterograde-to-retrograde reversal of protein transport adjacent to an axonal lesion. In experiments in which organelle transport was observed close to lesions in axons maintained in a medium compatible with intracellular function, 1.0 mM leupeptin inhibited neither the anterograde-to-retrograde nor the retrograde-to-anterograde reversal of organelle transport. In addition, in experiments in which conditions approximated those used to study protein transport, organelle transport away from the lesion was not inhibited by 1.0 mM leupeptin. A comparison of the morphology of rapidly transported organelles that underwent anterograde transport to the morphology of those that returned from a lesion (with or without the presence of leupeptin) provided no evidence that a morphological conversion was a necessary step in transport reversal.

Animals↗
PubMed1989

Junction between parent and daughter axons in regenerating myelinated nerve: properties of structure and rapid axonal transport.

The primary aim of this work was to investigate the properties of rapid axonal transport in regenerating myelinated axons in the sciatic nerve of Xenopus laevis, with particular attention to events at the junction between the proximal, intact axon (the "parent") and the distal, newly formed axon (the "daughter"). Morphological studies indicated that all myelinated axons initiated regeneration and that at least 80% of these axons regenerated at a rate of 1 mm/day or greater (20 degrees C). The ultrastructure of the junctional region was examined at regeneration times between 3 days and 20 weeks. The main qualitative change in the junctional axoplasm over this period was in its content of particulate organelles. At times up to 2 weeks regeneration, the junction contained abnormal numbers of 50 nm diameter vesicles and 10 nm granules. Between 2 and 5 weeks the junction showed in addition a peripheral rim of large membrane-bounded organelles around a central core of microtubules and neurofilaments. At longer times the numbers of large membrane-bounded organelles diminished and all junctions contained prominent accumulations of 10 nm granules. The rate of rapid axonal transport of protein was similar in parent and daughter axons. Compared to the parent axons, a 2-5 times greater amount of protein was deposited to a stationary phase in daughter axons. Specimens of nerve that were subjected to mechanical stress during the removal of the perineurium showed a large accumulation of rapidly transported protein in the region of the crush at regeneration times up to 40 days; some of the accumulated protein was subsequently transported retrogradely. Video microscopy of isolated axons supplied evidence that the transport deficit in mechanically stressed nerve was a partial block of anterograde vesicle transport, plus a reversal of anterograde transport, at the junction of parent with daughter axons. No structural changes were detected in mechanically stressed nerve. The results show that the junction between parent and daughter myelinated axons is a region with distinct morphology at which the dynamics of anterograde axonal transport may change dramatically.

Animals↗
PubMed1989

Loss of material from the retrograde axonal transport system in frog sciatic nerve.

Rapid axonal transport was studied in sciatic nerve preparations of the amphibian Xenopus laevis maintained in vitro at 23.0 +/- 0.2 degrees C. A pulse of [35S]methionine-labeled material was allowed to move in the anterograde direction until encountering a lesion, at which a portion of the pulse reversed directions and moved in the retrograde direction. By constricting the nerve during the course of the experiment, it was possible to prevent continuous return of label from the lesion, thus creating a retrogradely moving pulse that contained a defined quantity of radiolabel. Movement of both the anterograde and the retrograde pulse were monitored continuously for up to 24 h using a position-sensitive detector of ionizing radiation. The front and the back edge of the anterograde pulse were found to move at the rates of (mm/day) 179.9 +/- 3.9 (+/- SEM) and 149.9 +/- 5.9, respectively, and the front and the back edge of the retrograde pulse moved at the rates of 155.8 +/- 11.3 and 84.6 +/- 2.9, respectively. By comparison of the quantity of label lost to the stationary phase to the quantity of label calculated to have been present in the anterograde pulse, it was determined that 0.068 +/- 0.009 of the anterograde pulse is lost to each 3.18-mm region of nerve. Comparison of the quantity of label calculated to have been present in the retrograde pulse to that in the anterograde pulse revealed that 0.057 +/- 0.014 of the retrograde pulse is lost to each 3.18-mm region of nerve. It is concluded that protein originating in the cell body and which reverses its direction of transport at a lesion can be lost from the retrograde axonal transport system.

Animals↗
PubMed1988

The release of axonally transported material from an in vitro amphibian sciatic nerve preparation.

The rapid axonal transport of a pulse of [35S]methionine-labelled material was used to study the release of transported material from amphibian nerve maintained in vitro. Following creation of a moving pulse of activity in a dorsal root ganglion-sciatic nerve preparation, the ganglion was removed and the nerve placed in a three-compartment tray, the section of nerve in the middle compartment containing no truncated branches (unbranched section). All three compartments were filled with a saline solution that in some studies contained nonradioactive methionine (1.0 mmol/L). Analysis of studies in which nonradioactive methionine was absent revealed that labelled material appeared in the bathing solution of the end compartments that contained truncated branches, but not in the solution of the middle (unbranched) compartment. The quantity of label released in the branched compartments was approximately 6% of that remaining in the corresponding section of nerve following an 18-20 h incubation period. However, when nonradioactive methionine was present, all compartments showed an additional activity in the bathing solution of approximately 10% of that remaining in the nerve. In another study in which a position-sensitive detector of ionizing radiation was used to monitor progress of the pulse, it was found that activity did not enter the bathing solution of a compartment prior to the pulse of activity. It is concluded that in the absence of methionine from the bathing solution, axonally transported material is released only from regions of nerve that contain severed axons; however, the presence of methionine allows transported material to be released from nerve containing intact axons. Ultrafiltration studies and thin-layer chromatography revealed the majority of material released to be of low-molecular weight (less than 30,000 daltons) and not free [35S]methionine.

Animals↗
PubMed1986

The kinematics of turnaround and retrograde axonal transport.

Rapid axonal transport of a pulse of 35S-methionine-labelled material was studied in vitro in the sensory neurons of amphibian sciatic nerve using a position-sensitive detector. For 10 nerves studied at 23.0 +/- 0.2 degrees C it was found that a pulse moved in the anterograde direction characterized by front edge, peak, and trailing edge transport rates of (mm/d) 180.8 +/- 2.2 (+/- SEM), 176.6 +/- 2.3, and 153.7 +/- 3.0, respectively. Following its arrival at a distal ligature, a smaller pulse was observed to move in the retrograde direction characterized by front edge and peak transport rates of 158.0 +/- 7.3 and 110.3 +/- 3.5, respectively, indicating that retrograde transport proceeds at a rate of 0.88 +/- 0.04 that of anterograde. The retrograde pulse was observed to disperse at a rate greater than the anterograde. Reversal of radiolabel at the distal ligature began 1.49 +/- 0.15 h following arrival of the first radiolabel. Considerable variation was seen between preparations in the way radiolabel accumulated in the end (ligature) regions of the nerve. Although a retrograde pulse was seen in all preparations, in 7 of 10 preparations there was no evidence of this pulse accumulating within less than 2-3 mm of a proximal ligature; however, accumulation was observed within less than 5 mm in all preparations.

Animals↗
PubMed1986

A radiolabelled pulse for the simultaneous study of anterograde and retrograde axonal transport.

A technique is described for producing a pulse of [35S]methionine-labelled material which is axonally transported in amphibian sciatic nerve maintained in vitro. Using a position-sensitive detector of ionizing radiation, it is possible to continuously observe the movement of the pulse in the anterograde direction and, following turnaround at a ligature, the movement of a fraction of the pulse in the retrograde direction. Two sources of contaminant activity, which would otherwise interfere with observation of the pulse, are discussed and shown to be avoidable.

Animals↗
PubMed1985

Rapid axonal transport in Xenopus nerve in divalent cation free media.

An investigation was made of the effects of bathing media low in divalent cations on rapid axonal transport in the sciatic nerve of the amphibian Xenopus laevis. The anterograde transport of a pulse of [35S]methionine proteins was observed using a multiple proportional counter as the detector. Organelles undergoing anterograde and retrograde transport were detected by light microscopy. The structure of nerve fibers was examined by light and electron microscopy. There was no significant difference in the anterograde transport of proteins in nerves bathed in normal medium (NM) containing millimolar Ca2+ and Mg2+ and in those bathed in calcium-free medium (CaFM) containing Mg2+. The anterograde transport of labelled proteins continued at a normal velocity in nerves bathed in divalent cation free medium (DCFM) for at least 14 h. DCFM did cause some alterations in protein transport: the ratio of the plateau (following pulse passage) to the peak radioactivity was increased, the pulse amplitude decreased more rapidly, and the label continued to arrive at the distal end of the nerve for greater than 16 h. Anterograde and retrograde organelle transport continued normally for periods of greater than or equal to 4 h in fibres bathed in DCFM. All myelinated fibres became distorted within 4 h in DCFM. Similar distortion was rare in fibres bathed in CaFM. The results indicate that axonal transport in Xenopus is largely independent of lowered concentrations of divalent cations in the bathing medium. Those alterations in axonal transport that were produced by DCFM may have been secondary to morphological changes in the nerve fibres.

Animals↗
PubMed1979

A multiwire proportional chamber study of axoplasmic transport in frog sciatic nerve involving interruption of somatic supply.

A multiwire proportional chamber was used to detect axoplasmic transport in isolated spinal-cord-sciatic nerve preparations in which the nerve cell bodies were exposed to L-[35S]methionine. The detector collected radiation from a series of 6-mm segments of sciatic nerve for consecutive periods of 30 min for the duration of experiments lasting 16--23 h. The radioactivity of each segment showed an initial plateau at background level followed by a rise which was approximately linear through time. Plots of the time at which the rise in radioactivity took place against the position of each segment of the nerve yielded transport velocities for the most rapidly moving label; at room temperature (21--23 degrees C) these were typically 150 mm/24 h. Approximately 1.5 h after the addition of 5 mM colchicine to the bathing solution the slope of the radioactivity-time curve decreased for all segments of the nerve; this indicated that the method satisfactorily detected impaired axoplasmic transport. If the sciatic nerve were severed at the proximal end of the preparation at about 9 h after the radioactive front had been established, the slope of the radioactivity-time curve for each nerve segment subsequently changed abruptly. Plots of the time at which the transition occurred against position in the nerve yielded transport velocities which did not differ statistically from those of the radioactive front. This transition time is thought to indicate the time at which the fastest labelled material left each segment of nerve. In some experiments, an additional change in slope occurred, possibly indicating the departure of the slowest material from each segment.

Animals↗
PubMed1977

Prospective study of non-infiltrating carcinoma of the breast.

A long-term prospective study of non-infiltrating breast carcinoma is being carried out in order to study the natural history and proper management of such lesions with particular interest in patients treated solely by local excision. During an 11-year period, 175 patients with lobular Ca in situ and intraductal Ca have been followed. None has developed recurrent disease including 18 undergoing wide local excision only. Histologic examination revealed that 36% of mastectomy specimens showed multifocal lesions, whereas only one of the patients treated by wide local excision had more than one microscopic focus. For these reasons total mastectomy is recommended as the treatment of non-infiltrating breast carcinoma. Subsequent development of contralateral cancer has occurred in ten patients.

Adult↗
PubMed1976

Application of a multiwire proportional chamber to the detection of axoplasmic transport.

A new technique for the detection of the axoplasmic transport of beta-radioactively labelled materials is described wherein a multiwire proportional chamber is used to measure the distribution of activity along peripheral nerve fibers which are maintained in vitro. The operating principles of the chamber are described and basic construction parameters given. Potential radiolabels are discussed. Two types of studies were performed at room temperature in vitro using sciatic nerves of the amphibian Xenopus laevis: static and dynamic. In the static study the nerve ganglion was incubated for a suitable period of time in either L-(U-14C) leucine or L-(35S) methionine after which the ganglion was removed and the activity in the remaining nerve assayed with the chamber. In the dynamic study the nerve activity was assayed by the chamber while incubation proceeded so that a dynamic picture of transport could be observed. Using the second approach, transport rates were observed which are in agreement with others which have been reported in the literature. Some advantages and limitations of the technique are discussed.

Animals↗
PubMed1976

An automatic bolus injector for use in radiotracer studies of blood flow: design and evaluation.

An electromechanical device is described which automatically injects the radiotracer bolus used in the measurement of cerebral blood flow. It consists of two electronically controlled, solenoid operated syringes, one containing the radiotracer solution and the other heparinized saline. Results are presented which show that use of the automatic bolus injector in place of hand injection leads to an improvement in the precision of measured flow values. Additional advantages of the device are discussed.

Animals↗
PubMed1975

Patient exposures from film and xeroradiographic mammographic techniques.

Radiation exposures of several mammographic imaging systems, including (a) industrial film, xeroradiographic plates, the Du Pont Lo-Dose vacuum-cassette screen-film combination exposed with a molybdenum target tube and (b) xeroradiographic plates exposed with a tungsten target, were investigated with a thin-window ionization chamber and a range of exposures for different breast sizes was determined for each technique. The Lo-Dose system was found to provide high-quality diagnostic images with minimal patient exposure.

Health Physics↗