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R F Parshall

Publications and source records attributed to R F Parshall.

5 recordsLinked to original sources
PubMed1993

Structural synaptic correlate of long-term potentiation: formation of axospinous synapses with multiple, completely partitioned transmission zones.

Synapses were analyzed in the middle molecular layer (MML) and inner molecular layer (IML) of the rat dentate gyrus following the induction of long-term potentiation (LTP) by high-frequency stimulation of the medial perforant path carried out on each of 4 consecutive days. Potentiated animals were sacrificed 1 hour after the fourth high frequency stimulation. Stimulated but not potentiated and implanted but not stimulated animals served as controls. Using the stereological disector technique, unbiased estimates of the number of synapses per postsynaptic neuron were differentially obtained for various subtypes of axospinous junctions: For atypical (giant) nonperforated synapses with a continuous postsynaptic density (PSD), and for perforated ones distinguished by (1) a fenestrated PSD and focal spine partition, (2) a horseshoe-shaped PSD and sectional spine partition, (3) a segmented PSD and complete spine partition(s), and (4) a fenestrated, (5) horseshoe-shaped, or (6) segmented PSD without a spine partition. The major finding of this study is that the induction of LTP in the rat dentate gyrus is followed by a significant and marked increase in the number of only those perforated axospinous synapses that have multiple, completely partitioned transmission zones. No other synaptic subtype exhibits such a change as a result of LTP induction. Moreover, this structural alteration is limited to the terminal synaptic field of activated axons (MML) and does not involve an immediately adjacent one (IML) that was not directly activated by potentiating stimulation. The observed highly selective modification of synaptic connectivity involving only one particular synaptic subtype in the potentiated synaptic field may represent a structural substrate of the long-lasting enhancement of synaptic responses that characterizes LTP.

Animals↗
PubMed1991

Computer-aided geometric modeling of the human eye and orbit.

The author advocates, as a long-term development agenda for the profession, a shift in the working methods of medical illustrators from a two-dimensional image processing mode to a computer-aided design and drafting (CADD) mode. Existing CADD technology, which can make short work of the complex graphic construction problems of anatomical visualization, performs virtually all of its manipulations through systematic exercise of graphic geometry which illustrators tend to reduce to an intuitive, almost vestigial supplement to 2D image processing methods. The primary barrier to the immediate use of CADD is a lack of geometric database materials on anatomical component systems of the body. An on-going experimental project in modeling the human eye and orbit, utilizing a Silicon Graphics Iris workstation and Control Data Corporation's Integrated Computerized Engineering and Manufacturing (ICEM) software, exemplifies the preparatory work needed to create such database materials.

Computer Simulation↗
PubMedDate not supplied

Left ventricular shape-luminal pressure relationship. An open-chest study.

Left ventricular dimensions were measured in Cd2+ arrested (presumably diastolic), open-chest rats. Aortic pressure was maintained at 137 cm H2O (100 mm Hg) and left-ventricular (luminal) pressures were established and maintained at their chosen values, each by means of reservoir systems. The selected left-ventricular pressures were chosen to be within or to even broaden the range of conceivable diastolic pressures (-3 to 48 cm H2O). After in situ fixation with 4% formaldehyde and gelatin embedding, the hearts were serially sectioned in the apex base direction to obtain information at 11 levels (10, 20, . . . 90, 100%). Tracings of selected sections were made along the edge of the left ventricular lumen and the pericardial surface. Volumes, surface areas, and mean external and internal radii of the left ventricle were derived. To quantify the circularity of sections a form factor (FF) was introduced (FF = 1 for a circular cross-section and less than one for other shapes). Ventricular lengths, radial dimensions, endocardial and epicardial surface areas, and total and luminal volumes increased with the increasing intraventricular pressures; as expected, the wall simultaneously thinned. Though its appearance was altered by the wall thinning, the curving muscle fascicular pattern was present over the entire pressure range examined. Endocardial surface areas increased more than did the epicardial surface areas. The endocardial FF value increased (more circular) at each section level as the pressure increased. The epicardial FF relationship was apparently constant (0.798 +/- 0.014) for all section levels from 10% through 90%, regardless of luminal pressure. These results, when taken in conjunction with the results of our previous published studies, prompted the following speculation. The wall of the diastolic ventricle is a fluid-filled chamber with intramyocardial pressures that may be higher than ventricular pressures.

Animals↗