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PubMed1986

The architecture of actin filaments and the ultrastructural location of actin-binding protein in the periphery of lung macrophages.

A highly branched filament network is the principal structure in the periphery of detergent-extracted cytoskeletons of macrophages that have been spread on a surface and either freeze or critical point dried, and then rotary shadowed with platinum-carbon. This array of filaments completely fills lamellae extended from the cell and bifurcates to form 0.2-0.5 micron thick layers on the top and bottom of the cell body. Reaction of the macrophage cytoskeletons with anti-actin IgG and with anti-IgG bound to colloidal gold produces dense staining of these filaments, and incubation with myosin subfragment 1 uniformly decorates these filaments, identifying them as actin. 45% of the total cellular actin and approximately 70% of actin-binding protein remains in the detergent-insoluble cell residue. The soluble actin is not filamentous as determined by sedimentation analysis, the DNAase I inhibition assay, and electron microscopy, indicating that the cytoskeleton is not fragmented by detergent extraction. The spacing between the ramifications of the actin network is 94 +/- 47 nm and 118 +/- 72 nm in cytoskeletons prepared for electron microscopy by freeze drying and critical point drying, respectively. Free filament ends are rare, except for a few which project upward from the body of the network or which extend down to the substrate. Filaments of the network intersect predominantly at right angles to form either T-shaped and X-shaped overlaps having striking perpendicularity or else Y-shaped intersections composed of filaments intersecting at 120-130 degrees angles. The actin filament concentration in the lamellae is high, with an average value of 12.5 mg/ml. The concentration was much more uniform in freeze-dried preparations than in critical point-dried specimens, indicating that there is less collapse associated with the freezing technique. The orthogonal actin network of the macrophage cortical cytoplasm resembles actin gels made with actin-binding protein. Reaction of cell cytoskeletons and of an actin gel made with actin-binding protein with anti-actin-binding protein IgG and anti-IgG-coated gold beads resulted in the deposition of clusters of gold at points where filaments intersect and at the ends of filaments that may have been in contact with the membrane before its removal with detergent. In the actin gel made with actin-binding protein, 75% of actin-fiber intersections labeled, and the filament spacing between intersections is consistent with that predicted on theoretical grounds if each added actin-binding protein molecule cross-links two filaments to form an intersection in the gel.(ABSTRACT TRUNCATED AT 400 WORDS)

Actin Cytoskeleton↗

PubMed2000

Location of the vector of jaw muscle force in mammals.

Previous work has suggested that the third molar lies just in front of the point where the resultant vector of jaw muscle force, estimated from dissections, intersects the tooth row. This point meets the jaw such that the vector is 30% of jaw length from the jaw joint. Thus, the vector divides the jaw in the ratio of 3:7 when measurements are taken perpendicular to the vector. In practice, however, distances along mammalian jaws are typically measured on an easily determined line such as a line from one end of the tooth row to the other. The position of the jaw joint is then projected onto this line. As a rule, such a line is not perpendicular to the vector and so the distance from the projection of the joint, out to the rear of the third molar (and the vector's intersection), is different in different mammals. Rarely is this distance 30% of total jaw length. However, when the location of the vector's intersection is measured along the tooth row, this position varies directly with the inclination of the vector; a vector inclined posteriorly intersects the tooth row far from the projection of the joint and an anterior vector's intersection is relatively close. Only a vector perpendicular to the line from one end of the tooth row to the other intersects at 30%. This obvious point suggests a way to test the above hypotheses when the inclination of the vector is not known exactly. The predicted relationship between the distance to the molar, as a percentage of the total jaw length, and the approximate inclination of the vector derived from muscle weights (posterior or anterior depending on whether the temporalis or the masseter/pterygoid, respectively, is dominant) was observed in a sample of 46 different mammals.

Animals↗

PubMed2006

Effects of substrate geometry on growth cone behavior and axon branching.

At the leading edge of a growing axon, the growth cone determines the path the axon takes and also plays a role in the formation of branches, decisions that are regulated by a complex array of chemical signals. Here, we used microfabrication technology to determine whether differences in substrate geometry, independent of changes in substrate chemistry, can modulate growth cone motility and branching, by patterning a polylysine grid of narrow (2 or 5 microm wide) intersecting lines. The shape of the intersections varied from circular nodes 15 microm in diameter to simple crossed lines (nodeless intersections). Time-lapse recordings of cultured hippocampal neurons showed that simple variations in substrate geometry changed growth cone shape, and altered the rate of growth and the probability of branching. When crossing onto a node intersection the growth cone paused, often for hours, and microtubules appeared to defasciculate. Once beyond the node, filopodia and lamellipodia persisted at that site, sometimes forming a collateral branch. At nodeless intersections, the growth cone passed through with minimal hesitation, often becoming divided into separate areas of motility that led to the growth of separate branches. When several lines intersected at a common point, growth cones sometimes split into several subdivisions, resulting in the emergence of as many as five branches. Such experiments revealed an intrinsic preference for branches to form at angles less than 90 degrees . These data show that simple changes in the geometry of a chemically homogeneous substrate are detected by the growth cone and can regulate axonal growth and the formation of branches.

Animals↗

PubMed1993

Molecular skins: a new concept for quantitative shape matching of a protein with its small molecule mimics.

A novel analytical method for comparing molecular shapes by optimizing the intersection of molecular "SKINS" has been developed. This method provides a quantitative measure of the shape similarity by maximizing the intersection volume of molecular surfaces with a finite thickness; a molecular skin. We report shape matching of a small tripeptide inhibitor (DFKi) of elastase class proteins with the 56 residue turkey ovomucoid inhibitor (TOMI). To match a large elastase inhibitor such as TOMI with a small inhibitor or drug, we found that it is necessary to use a skin match rather than molecular volume. Skin based comparisons of TOMI protein with DFKi successfully found the alignment expected from comparison of their respective crystallographic complexes with elastase (i.e. HLE/TOMI complex and PPE/tripeptide complex). In the skin comparison of the tripeptide with the TOMI protein, blind searching for skin matches involved optimization of the skin intersection from 172 starting positions randomly selected from a set of 500 points on the TOMI van der Waals surface [within 9.5 A of the Leu-18 on the TOMI binding loop (1 point/A2)]. The tripeptide center of mass was placed at these points and its orientation was randomized before optimization was initiated. The best skin intersection, 86.4 A3, was found three times and corresponds to the experimental alignment. The next best skin intersection was 78.1 A3 giving a discrimination factor in this case of 10%. Searches over the entire surface of the TOMI protein did not identify any new matches with skin intersection greater than 78.1 A3. Matching the DFKi with a TOMI structure relaxed from its crystal conformation by molecular dynamics gives similar results.

Amino Acid Sequence↗

PubMed2004

Auditing concept categorizations in the UMLS.

The Unified Medical Language System (UMLS) integrates about 880,000 concepts from 100 biomedical terminologies. Each concept is categorized to at least one semantic type of the Semantic Network. During the integration, it is unavoidable that some categorization errors and inconsistencies will be introduced. In this paper, we present an auditing technique to find such errors and inconsistencies. Our technique is based on an expert reviewing the pure intersections of meta-semantic types of a metaschema, a compact abstract view of the UMLS Semantic Network. We use a divide and conquer approach, handling differently small pure intersections and medium to large pure intersections. By using this approach, we limit the number of concepts reviewed, for which we expect a high percentage of errors. We reviewed all concepts in 657 pure intersections containing one to 10 concepts. Various kinds of errors are identified and the analysis of the results are presented in the paper. Also, we checked the pure intersections containing more than 10 concepts for their semantic soundness, where the semantically suspicious pure intersections are presented in the paper and their concepts are reviewed.

Abstracting and Indexing↗

PubMed2006

How accurately can the diffusion profiles indicate multiple fiber orientations? A study on general fiber crossings in diffusion MRI.

The q-space imaging techniques and high angular resolution diffusion (HARD) imaging have shown promise to identify intravoxel multiple fibers. The measured orientation distribution function (ODF) and apparent diffusion coefficient (ADC) profiles can be used to identify the orientations of the actual intravoxel fibers. The present study aims to examine the accuracy of these profile-based orientation methods by comparing the angular deviations between the estimated local maxima of the profiles and the real fiber orientation for a fiber crossing simulated with various intersection angles under different b values in diffusion-weighted MRI experiments. Both noisy and noise-free environments were investigated. The diffusion spectrum imaging (DSI), q-ball imaging (QBI), and HARD techniques were used to generate ODF and ADC profiles. To provide a better comparison between ODF and ADC techniques, the phase-corrected angular deviations were also presented for the ADC method based on a circular spectrum mapping method. The results indicate that systematic angular deviations exist between the actual fiber orientations and the corresponding local maxima of either the ADC or ODF profiles. All methods are apt to underestimation of acute intersection and overestimation of obtuse intersection angle. For a typical slow-exchange fiber crossing, the ODF methods have a non-deviation zone around the 90 degrees intersection. Before the phase-correction, the deviation of ADC profiles approaches a peak at the 90 degrees intersection, while after the correction the ADC deviations are significantly reduced. When the b factor is larger than 1000 s/mm2, the ODF methods have smaller angular deviations than the ADC methods for the intersections close to 90 degrees . QBI method demonstrates a slight yet consistent advantage over the DSI method under the same conditions. In the noisy environment, the mean value of the deviation angles shows a high consistency with the corresponding deviation in the nose-free condition.

Algorithms↗

PubMed1999

Anterior cruciate ligament and intercondylar notch in the coronal oblique plane: anatomy complemented by magnetic resonance imaging in cruciate ligament-intact knees.

We assessed the anatomy of the anterior cruciate ligament (ACL) and femoral intercondylar notch on cryosections from one cadaveric knee specimen in the coronal oblique plane oriented parallel to the intercondylar roof. We determined the course of the ACL, the widths of the cruciate ligaments at intersection, and the intercondylar notch configuration on coronal oblique plane magnetic resonance images in 51 adult cruciate ligament-intact knees (25 women, 26 men; age range, 16 to 47 years). The intercondylar notch widths were measured at the notch entrance, at the intersection of the ACL and posterior cruciate ligament (PCL), and at the notch outlet. In the coronal oblique plane, the ACL exhibited a diagonal course from the central and medial part of the anterior intercondylar area of the tibia distally, across the lateral third of the intercondylar notch, to the intercondylar surface of the lateral femoral condyle proximally. At the cruciate ligament intersection, the absolute widths of the ACLs measured on average 6.1+/-1.1 mm in men and 5.2+/-1.0 mm in women representing 31.9% and 31.1% of the ACL/central intercondylar notch width ratios. The absolute widths of the PCLs measured on average 9.6+/-1.3 mm in men and 8.5+/-1.3 mm in women representing 50.4% and 51.4% of PCL/central intercondylar notch width ratios. On average for both groups, men and women, the absolute widths of the PCLs were significantly larger than the absolute widths of the ACLs. However, the relative widths of the cruciate ligaments with respect to corresponding intercondylar notch widths were not significantly different. In the coronal oblique plane, the intercondylar notch widths showed on average a significant decrease from posterior to intersection and from intersection to anterior. At notch outlet, the mean notch width measured 21.4 mm in men and 18.5 mm in women. At intersection, the mean notch width measured 19.1 mm in men and 16.6 mm in women. At notch entrance, the notch width measured 14.6+/-1.8 mm in men and 12.7+/-2.1 mm in women. We recommend magnetic resonance tomography of the knee in the coronal oblique plane oriented parallel to the intercondylar roof as the imaging modality of choice to visualize accurately the anatomic diagonal course of the ACL and its relation to the intercondylar notch and posterior cruciate ligament complex.

Adolescent↗

PubMedDate not supplied

Three-dimensional echocardiography: limitations of apical biplane imaging for measurement of left ventricular volume.

A new three-dimensional echocardiographic system creates a "line of intersection" display to allow precise and known positioning of echocardiographic images. Our purpose was to determine whether use of the line-of-intersection display will improve positioning of the apical four-chamber and apical two-chamber views and thereby improve the agreement between estimates of left ventricular volume by apical biplane echocardiography and cineventriculography. Unguided and line of intersection-guided apical biplane views were obtained in 31 patients immediately before cardiac catheterization and single-plane cineventriculography. In 15 patients the line-of-intersection display was used to measure the position of the image plane in studies of unguided and guided methods. Linear regression and limits of agreement analysis were used to assess the agreement between cineventriculographic volumes and echocardiographic volumes determined from each set of images. The Wilcoxon test was used to compare guided and unguided image positioning. The line-of-intersection display improved four-chamber and two-chamber view positioning closer to the center of the ventricle and rotation closer to orthogonal positioning. Guided-image positioning was not able to correct displacement of the ultrasound beam anterior to the ventricular apex without deterioration of image quality in most patients. Despite improvements in image plane positioning, the agreement between echocardiographic and cineventriculographic volumes was unchanged. For end-diastole views, the unguided images had an r value = 0.84, standard error of the estimate of +/- 23.0 cc, and limits of agreement of +/- 62.4 cc. Corresponding values for the guided images at end diastole were r = 0.85, standard error of the estimate of +/- 22.9 cc, and limits of agreement of +/- 60.8 cc. At end systole the unguided results were r = 0.91, standard error of the estimate of 16.8 cc, and limits of agreement of +/- 52.2 cc. The line-of-intersection guiding of image plane positioning can improve apical image positioning but does not improve the agreement between apical biplane echocardiographic and cineventriculographic left ventricular volumes. The optimal apical imaging window is frequently occluded by the rib cage, resulting in a decrease in image quality. This reduction of image quality, combined with assumptions of left ventricular geometry, limit the accuracy of estimates of left ventricular volume from apical biplane echocardiography.

Adult↗

PubMed2001

Potential energy surface crossings and the mechanistic spectrum for intramolecular electron transfer in organic radical cations.

The structure of the potential energy surface for the intramolecular electron transfer (IET) of four different model radical cations has been determined by using reaction path mapping and conical intersection optimization at the ab initio CASSCF level of theory. We show that, remarkably, the calculated paths reside in regions of the ground-state energy surface whose structure can be understood in terms of the position and properties of a surface crossing between the ground and the first excited state of the reactant. Thus, in the norbornadiene radical cation and in an analogue compound formed by two cyclopentene units linked by a norbornyl bridge, IET proceeds along direct-overlap and super-exchange concerted paths, respectively, that are located far from a sloped conical intersection point and in a region where the excited-state and ground-state surfaces are well separated. A second potential energy surface structure has been documented for 1,2-diamino ethane radical cation and features two parallel concerted (direct) and stepwise (chemical) paths. In this case a peaked conical intersection is located between the two paths. Finally, a third type of energy surface is documented for the bismethyleneadamantane radical cation and occurs when there is, effectively, a seam of intersection points (not a conical intersection) which separates the reactant and product regions. Since the reaction path cannot avoid the intersection, IET can only occur nonadiabatically. These IET paths indicate that quite different IET mechanisms may operate in radical cations, revealing an unexpectedly enriched and flexible mechanistic spectrum. We show that the origin of each path can be analyzed and understood in terms of the one-dimensional Marcus-Hush model.

Journal Article↗

PubMed2002

Quenching of tryptophan (1)(pi,pi*) fluorescence induced by intramolecular hydrogen abstraction via an aborted decarboxylation mechanism.

CASSCF computations show that the hydrogen-transfer-induced fluorescence quenching of the (1)(pi,pi*) excited state of zwitterionic tryptophan occurs in three steps: (1) formation of an intramolecular excited-state complex, (2) hydrogen transfer from the amino acid side chain to the indole chromophore, and (3) radiationless decay through a conical intersection, where the reaction path bifurcates to a photodecarboxylation and a phototautomerization route. We present a general model for fluorescence quenching by hydrogen donors, where the radiationless decay occurs at a conical intersection (real state crossing). At the intersection, the reaction responsible for the quenching is aborted, because the reaction path bifurcates and can proceed forward to the products or backward to the reactants. The position of the intersection along the quenching coordinate depends on the nature of the states and, in turn, affects the formation of photoproducts during the quenching. For a (1)(n,pi*) model system reported earlier (Sinicropi, A.; Pogni, R.; Basosi, R.; Robb, M. A.; Gramlich, G.; Nau, W. M.; Olivucci, M. Angew. Chem., Int. Ed. 2001, 40, 4185-4189), the ground and the excited state of the chromophore are hydrogen acceptors, and the excited-state hydrogen transfer is nonadiabatic and leads directly to the intersection point. There, the hydrogen transfer is aborted, and the reaction can return to the reactant pair or proceed further to the hydrogen-transfer products. In the tryptophan case, the ground state is not a hydrogen acceptor, and the excited-state hydrogen transfer is an adiabatic, sequential proton and electron transfer. The decay to the ground state occurs along a second reaction coordinate associated with decarboxylation of the amino acid side chain and the corresponding aborted conical intersection. The results show that, for (1)(pi,pi*) states, the hydrogen transfer alone is not sufficient to induce the quenching, and explain why fluorescence quenching induced by hydrogen donors is less general for (1)(pi,pi*) than for (1)(n,pi*) states.

Fluorescence↗

PubMed2002

Cyclooctatetraene computational photo- and thermal chemistry: a reactivity model for conjugated hydrocarbons.

We use ab initio CASSCF and CASPT2 computations to construct the composite multistate relaxation path relevant to cycloocta-1,3,5,7-tetraene singlet photochemistry. The results show that an efficient population of the dark excited state (S(1)) takes place after ultrafast decay from the spectroscopic excited state (S(2)). A planar D(8)(h)-symmetric minimum represents the collecting point on S(1). Nonadiabatic transitions to S(0) appear to be controlled by two different tetraradical-type conical intersections, which are directly accessible from the S(1) minimum following specific excited-state reaction paths. The higher-energy conical intersection belongs to the same type of intersections previously documented in linear and cyclic conjugated hydrocarbons and features a triangular -(CH)(3)- kink. This point mediates both cis --> trans photoisomerization and cyclopropanation reactions. The lowest energy conical intersection has a boat-shaped structure. This intersection accounts for production of semibullvalene or for double-bond shifting. The mapping of both photochemical and thermal reaction paths (including also Cope rearrangements, valence isomerizations, ring inversions, and double-bond shifting) has allowed us to draw a comprehensive reactivity scheme for cyclooctatetraene, which rationalizes the experimental observations and documents the complex network of photochemical and thermal reaction path interconnections. The factors controlling the selection and accessibility of a number of conjugated hydrocarbon prototype conical intersections and ground-state relaxation channels are discussed.

Journal Article↗

PubMed2005

Time-dependent quantum wave-packet description of the 1pi sigma* photochemistry of phenol.

The photoinduced hydrogen elimination reaction in phenol via the conical intersections of the dissociative 1pi sigma* state with the 1pi pi* state and the electronic ground state has been investigated by time-dependent quantum wave-packet calculations. A model including three intersecting electronic potential-energy surfaces (S0, 1pi sigma*, and 1pi pi*) and two nuclear degrees of freedom (OH stretching and OH torsion) has been constructed on the basis of accurate ab initio multireference electronic-structure data. The electronic population transfer processes at the conical intersections, the branching ratio between the two dissociation channels, and their dependence on the initial vibrational levels have been investigated by photoexciting phenol from different vibrational levels of its ground electronic state. The nonadiabatic transitions between the excited states and the ground state occur on a time scale of a few tens of femtoseconds if the 1pi pi*-1pi sigma* conical intersection is directly accessible, which requires the excitation of at least one quantum of the OH stretching mode in the 1pi pi* state. It is shown that the node structure, which is imposed on the nuclear wave packet by the initial preparation as well as by the transition through the first conical intersection (1pi pi*-1pi sigma*), has a profound effect on the nonadiabatic dynamics at the second conical intersection (1pi sigma*-S0). These findings suggest that laser control of the photodissociation of phenol via IR mode-specific excitation of vibrational levels in the electronic ground state should be possible.

Journal Article↗

PubMed2005

Escape from the double cone: optimized descriptions of the seam space using gateway modes.

The conceptual description of nuclear dynamics near a conical intersection generally focuses on the branching plane, the two-dimensional subspace in which the conical topography is evinced, to the exclusion of the seam coordinates, the remaining internal nuclear coordinates. Establishing the limits of the utility of this assumption is an important issue in nonadiabatic dynamics. To accomplish this a careful treatment of the nuclear dynamics near conical intersections is required. The coordinate systems generally available for describing conical intersections are not optimal for such studies. In this work we extend a perturbative description of a conical intersection to describe more general seam spaces. We develop a coordinate system that segregates the interactions coupling the branching plane to the seam space into a set of gateway modes. The size of this set does not increase with the size of the molecule. The gateway modes are illustrated for the 1,2 1A conical intersections in NH3. The connection between the gateway modes and the optimum coordinate system for locating and characterizing seam confluences, intersections of two branches of the same seam, is discussed.

Journal Article↗

PubMed2000

A new screening measure to identify potential carbon monoxide hotspots.

To demonstrate conformity of transportation projects to National Ambient Air Quality Standards in accordance with State Implementation Plans, the U.S. Environmental Protection Agency (EPA) uses intersection level of service (LOS) as one of its major criteria for screening for potential carbon monoxide (CO) hotspots. Although intersection LOS is a measure of traffic volume, signal timing, and related congestion and delay, the assigned level reflects only the computed averaged stopped delay (ASD) per vehicle at the intersection. Thus, intersections can often operate at the same LOS but produce vastly different levels of predicted CO concentrations. For example, a two-lane approach operating at LOS D will produce very different levels of CO than a five-lane approach also operating at LOS D. This study explores the effectiveness of the LOS D criterion as a screen for identifying potential CO hotspots. The study results indicate that LOS is a poor predictor of potential CO hotspots when compared to results generated with the EPA-recommended micro-scale model CAL3QHCr. To more consistently screen out those intersections that will not be identified as CO hotspots using the micro-scale models, a new criterion, equivalent red-time vehicles (ERTV), is introduced. The modeling results using ERTV suggest that it is a more robust measure for identifying potential CO hotspots, and conversely, screening out those intersections that are not likely to be identified as hotspots using micro-scale simulation results.

Air Pollutants, Occupational↗

PubMed2005

Structure of toluene6.4-ZSM-5 and the toluene disproportionation reaction on ZSM-5.

The structure of a high-loading complex of ZSM-5 with 6.4 toluene molecules per unit cell has been determined by single-crystal X-ray diffraction. At least three kinds of toluene molecules were identified in the unit cell. Two disordered toluene molecules were located at the intersection of the straight and sinusoidal channels, the third in the sinusoidal channel. One (TOL1) of the two toluene orientations at the intersection was similar to that of p-dichlorobenzene at the intersection in high-loaded H-ZSM-5/p-xylene (hereafter 8PARA) and high-loaded H-ZSM-5/p-dichlorobenzene (hereafter 8PDCB) complexes, respectively. The other toluene orientation (TOL2) at the intersection was similar to those of p-xylene or p-dichlorobenzene at the intersection in the low-loaded p-dichlorobenzene complex (hereafter 2.6PDCB). A third toluene orientation (TOL3) existed in the sinusoidal channel; its orientation was similar to those of p-xylene and p-dichlorobenzene in the sinusoidal channels in 8PARA and 8PDCB complexes, respectively. If the occupancy of TOL2 at the intersection increases with temperature, TOL2 will connect with TOL3 in the sinusoidal channel and form the intermediate diphenylmethane.

Journal Article↗

PubMed2001

Increasing motorist compliance and caution at stop signs.

This study evaluated strategies to improve motorist compliance and caution at three stop-sign-controlled intersections with a history of motor vehicle crashes. The primary intervention was a light-emitting diode (LED) sign that featured animated eyes scanning left and right to prompt drivers to look left and right for approaching traffic. Data were scored from videotape on the percentage of drivers coming to a complete stop and the percentage of drivers looking right before entering the intersection. Observational data were collected on the percentage of right-angle conflicts (defined as braking suddenly or swerving from the path to avoid an intersection crash). The introduction of the LED sign according to a multiple baseline across the three intersections was associated with an increase in the percentage of vehicles coming to a complete stop at all three intersections and a small increase in the percentage of drivers looking right before entering the intersections. Conflicts between vehicles on the major and minor road were also reduced following the introduction of the animated eyes prompt.

Adult↗

PubMed2004

Failure of a traffic control "fatality" sign to affect pedestrians' and motorists' behavior.

The behavior of 643 pedestrians and 1749 motorists at two signal-controlled intersections was observed over a 2-mo. period of observation in March and November. One intersection had a coffin-shaped traffic sign with the wording "Fatality" erected during the first month of observation (March). The second intersection was identical in traffic and pedestrian volume but lacked a "Fatality" sign in either March or November. "Fatality" signs are erected and maintained by the City of Edmonton for 6 mo. whenever a pedestrian death has occurred, and they are intended to raise the awareness of both pedestrians and motorists concerning the risks at dangerous intersections. This sign had been removed for nearly 3 mo. when a follow-up observation was made in November. While female pedestrians and pedestrians over the age of 50 years showed greater caution at both intersections, the presence or absence of the "Fatality" sign had no statistically significant influence on safety. Similarly, the presence or absence of a sign did not significantly influence motorists' behavior. Of motorists 7.6% ran either amber or red traffic control lights at the two intersections. The "Fatality" sign did not affect the rates of these violations.

Accidents, Traffic↗

PubMed2000

Migration pathways of hypodermically injected technetium-99m in dogs.

Hypodermic injection of technetium-99m (99mTc-pertechnetate) at points of low electrical resistance give rise to rapid, longitudinal, and progressive diffusion of the radioactive tracer. We assessed the effect of cutaneous incisions that did not intersect the migration trajectory of 99mTc-pertechnetate and the re-establishment of pathways after the suture of incisions that intersected the migration trajectory. Linear and rapid migration of 99mTc-pertechnetate was not altered or prevented by incisions that did not intersect the migration pathway. Different patterns of 99mTc-pertechnetate spread were found when incisions intersected the radioactive pathways until restoration of the normal migration pathway observed in undamaged skin occurred. In all experiments in which migration of 99mTc-pertechnetate was observed, lavage of surgical wounds was followed by disappearance of the 99mTc-pertechnetate migration observed around the suture. Linear migration of the tracer was not observed when the incision was left uncovered, filled with petroleum jelly, or with a solid silicone sheet, but it was seen when non-sutured incisions were filled with transonic or silicone gel or covered with a solid silicone sheet parallel to the cutaneous plane. These data show that after a cutaneous incision that intersected the diffusion trajectory of the radioactive tracer, linear migration of 99mTc-pertechnetate hypodermically injected at points of low electrical resistance was restored before healing of the cutaneous incision and was independent of incisions made on the skin not overlying the radioactive pathway. A mechanism similar to that of capillary electrophoresis is suggested to explain the hypodermic diffusion of inert particles through specific and constant linear pathways.

Animals↗