Search PubMed⌕ Search

Biomedical subjects

R E Snyder

Publications and source records attributed to R E Snyder.

11 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↗
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↗
PubMedDate not supplied

Relationships between the rapid axonal transport of newly synthesized proteins and membranous organelles.

Rapid axonal transport is generally viewed as being exactly analogous to the secretory process in nonneuronal cells. The cell biology of rapid axonal transport is reviewed, the central concern being to explore those aspects that do not fit into the general secretory model and which may thus represent specific neuronal adaptations. Particular attention is paid to the relationship between the transport of newly synthesized proteins and of the membranous organelles that act as carriers. Sites in the transport sequence at which the behavior of axonal transport may differ from the secretory model are at the initiation of axonal transport at the trans-side of the Golgi apparatus, within the axon where molecules are deposited from the moving phase to a stationary phase, and at nerve terminals or axonal lesions where transport reversal takes place.

Animals↗
PubMedDate not supplied

Protein loss from axonal transport occurs without diminution of vesicle traffic.

Protein loss from the rapid anterograde axonal transport system of amphibian sensory nerve fibers was compared with the numbers and sizes of anterogradely transported vesicles in the axons. Protein was found to be lost at a rate of approximately 2% per millimeter of nerve traversed. However, no changes were observed in either the numbers or sizes of vesicles in the nerve at two locations separated by 60-75 mm. The results show that protein loss is not explained as a loss of vesicles from the transport system nor by a reduction in vesicle size.

Animals↗