Small Tracer Research Articles

Evidence for a tight blood‐labyrinth barrier

The entry of a small tracer ion (FW 135.6) from blood into perilymph and cerebrospinal fluid (CSF) has been monitored using ion‐selective electrodes. The tracer, trimethylphenylammonium (TMPA) can be detected in extremely low concentrations (< 1 μm) by electrodes, allowing entry to be accurately quantified. Electrodes were sealed into the cochlea to ensure that artifactual fluid leakages did not distort the results. A constant level of TMPA in plasma (approximately 0.5 mM) was maintained by continuous venous infusion of tracer. TMPA entry into CSF was extremely slow, reaching only 13% of the plasma level within 90 min (n = 3). Tracer entered perilymph even more slowly, reaching 6.5% (n = 5) and 3.7% (n = 5) of the plasma level in 90 min for ST and SV, respectively. The slow entry of such a small ion into perilymph demonstrates the existence of a tight barrier between blood and perilymph, and eliminates the possibility that perilymph is generated by mechanisms such as ultrafiltration. In two animals where bleeding was noted at the electrode insertion site, a much more rapid rate of tracer entry was recorded, probably as a result of plasma leakage into perilymph. Treatment with epinephrine (giving a brief blood pressure increase) also opens the barrier, allowing rapid tracer entry.

Measurements of laser plasma coronal conditions and thermal transport with time-resolved x-ray spectroscopy.

This paper presents a detailed characterization of the plasma conditions near the critical density of a laser-produced plasma. Solid spherical plastic targets with small aluminum tracer dots buried below overcoated plastic layers have been uniformly illuminated with green laser light at irradiances of ${10}^{14}$--${10}^{15}$ W/${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$. Time-resolved temperature and density profiles were obtained by using x-ray emission spectroscopy. Detailed comparisons with hydrodynamic simulations show that the thermal transport is well characterized by a flux limit of 0.1.

Subcortical projections to the pontine nuclei in the cat

In a systematic attempt to trace all projections from the brainstem and diencephalon to the pontine nuclei of the cat, implantations and injections of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) or Fluoro-Gold were placed in the pontine nuclei of 21 cats. In most of the cases there was no evidence of spread of tracer outside the pontine nuclei. Retrogradely labeled cells in the brainstem and diencephalon were carefully mapped and counted. The number labeled cells in the brainstem and diencephalon ranged from 24 in cases with very small implantations to 3,490 in cases with large injections in the pontine nuclei (counts from every fifth section). The labeled cells are located bilaterally with an ipsilateral preponderance. After large injections, 25-38% of the labeled cells were located in the brainstem reticular formation, 10-16% in the pretectal nuclei, 10-15% in the hypothalamus, 7-9% in the zona incerta, 3-9% in the fields of Forel, 4-5% in the nucleus locus coeruleus, 3-5% in the ventral lateral geniculate body, 2-4% in the superior colliculus, 3% in the periaqueductal gray, and 14-15% in other parts of the brainstem. Judging from cases with small tracer deposits entirely confined to the pontine nuclei, there appear to be two types of subcortical inputs: Projections from the reticular formation, the nucleus locus coeruleus, the periaqueductal gray, and the raphe nuclei are widespread, presumably reaching all parts of the pontine nuclei, while projections from a diversity of other sources are localized, reaching limited parts of the pontine nuclei only or predominantly.

The effect of a low pH saline perfusate upon the integrity of the energy-depleted rat blood-brain barrier.

The effect of a low pH perfusate upon the integrity of the rat blood-brain barrier was studied using an in situ supravital brain perfusion technique in which high-energy phosphates are depleted. Control animals were perfused for 10 min with a Ringer's salt solution containing the metabolic inhibitor 2,4-dinitrophenol (DNP) and adjusted to a pH of 7.4. In two separate experimental groups the perfusate, consisting of either the same medium as the controls or with additional buffering from Tris maleate, was switched after 5 min at a pH of 7.4, to a medium adjusted to pH 5.5 with lactic acid. Following a total perfusion time of 10 min, the integrity of the blood-brain barrier was assessed using the small molecular weight tracer [14C]mannitol. The cerebral perfusate flow rates (CPFR) after 10 min of perfusion were also determined in the three groups by perfusing for 40 s with [14C]iodoantipyrine. In each group, mannitol was excluded from the tissue of the brain to the same degree as has been previously reported in vivo, indicating an intact blood-brain barrier. There was also no significant pH-dependent change in CPFR. Ultrastructural examination of animals that had been perfusion fixed following in situ perfusion revealed no obvious differences between the cerebral endothelium of the control and low pH perfused animals. These results demonstrate that in the absence of energy-producing metabolism a perfusate pH of 5.5 is insufficient to disrupt the blood-brain barrier.

Three-dimensional structures in laminar natural convection in a cubic enclosure

The thermal convection in a cubic cavity, with two opposite vertical walls kept at prescribed temperatures, is investigated experimentally. The Rayleigh numbers ranged from 10 4 to 2 × 10 7 and the Prandtl numbers from 5.8 to 6 × 10 3. The velocity and vorticity fields are shown. The temperature fields were visualized with the help of liquid crystals suspended as small tracer particles in the medium. It is observed that convection in the cavity is strongly three-dimensional. The streamlines spiral from the foci on the walls toward the foci in the vertical midplane and vice versa. The disappearance of one of the vortices midway between the center and the front or back wall is observed for RA > 6 × 10 4. The topological structures are discussed. The experimental observations are compared with numerical calculations found in the literature.

Circulation time for pseudoplastic liquids in a vessel equipped with a variety of helical ribbon impellers.

Measurements of the circulation time for pseudoplastic liquids in an agitated vessel of 0.128 m diameter equipped with a variety of helical ribbon impellers were carried out in a wide range of apparent Reynolds number by means of a small tracer particle. Seven impellers of different dimensions (clearance between blade and vessel wall, impeller pitch and blade width) were employed in this work.Whilst previous investigators have suggested that the dimensionless circulation time is independent of the Reynolds number, a number of data obtained in this work have proved that the dimensionless circulation time of pseudoplastic liquids with a helical ribbon impeller decreases slightly with decrease in the apparent Reynolds number in the laminar flow region. It was also found that the circulation time increases as the liquid shear-thinning property increases. These results are explained by considering the relation between the motion of a tracer particle and the non-uniformity in viscosity created in a vessel.

Introduction into the study of translational diffusion by laser techniques

AbstractWe give a short description of the holographic grating technique for determining small tracer diffusion coefficients of photo labeled polymers and the quasielastic light scattering technique for studying polymer polymer interdiffusion. For applications in polymer systems we refer to the recent literature.

Equivalent pore estimate for the alveolar-airway barrier in isolated dog lung

In high-pressure pulmonary edema, lung interstitial and air space edema liquids have equal protein concentrations (Am. J. Physiol. 231: 1466, 1976). This suggests that the alveolar-airway barrier separating the air and interstitial spaces is relatively unrestrictive, even without apparent epithelial injury. To estimate the equivalent pore population of the alveolar-airway barrier we inflated each of 18 isolated dog lung lobes for 1 h with a solution of colored tracer of uniform radius. Tracer radii ranged from 1.3 to 405 nm. After freezing the lobes in liquid N2, we measured interstitial tracer concentrations in frozen perivascular cuffs or in samples thawed after dissection from frozen cuffs. Relative to the concentrations instilled, interstitial concentrations ranged from 0.34 for the smallest particles (1.3 and 3.5 nm radius) to zero for particles with radii of 405 nm. From the results we designed a pore model of the alveolar-airway barrier to reproduce the concentrations we measured. No single-pore model could be obtained, although a three-pore model fit the data well. The model results predict that pores with radii of 1, 40, and 400 nm would account for 68, 30, and 2% of total liquid flux, respectively. The majority of liquid flux (68%) would occur through passageways smaller than the smallest tracer we used (1.3 nm radius). We believe the alveolar-airway barrier consists not only of tight intercellular junctions that allow passage of only water and electrolytes but also of a smaller number of large leaks that allow passage of particles up to nearly 400 nm in radius.

Cerebellar cortical and nuclear afferents from the Edinger-Westphal nucleus in the cat

The cerebellar projection from the Edinger-Westphal nucleus was studied in the cat by means of retrograde transport of the wheat germ agglutinin-horseradish peroxidase complex. The present findings give evidence that the flocculus is the main terminal area. However, small tracer implants and injections into various parts of the cerebellar nuclei and cortex revealed projections also to the fastigial and interposed nuclei and to most parts of the anterior and posterior lobe cortices. The projecting neurons are small and located bilaterally throughout the Edinger-Westphal nucleus. No topical differences between the projections to different parts of the cerebellum were found.

Fiber Orientation in Fiber Suspension Flow

We investigate experimentally the orientation of the fibers in the flow of both Newtonian and viscoelastic fluids through a parallel plate channel and a channel with an abrupt contraction. We obtain quantitatively the development of the fiber orientation from initial orientation to stable equilibrium orientation along the channel and the variation of orientation in the direction of the channel width. We also study, in the flow through a channel with an abrupt contraction, the fiber orientation along the stream lines which can be found as the path lines of small tracer particles suspended in the fluid. The relation between the fiber orientation and the velocity field is examined. The effects of shear thinning and elasticity on the fiber orientation are also discussed by comparing the results in the viscoelastic flow with those in the Newtonian flow. The conclusions are summarized as follows : (1) The fibers orient well along the stream lines with an increase in viscoelasticity in both a parallel plate channel and a channel with an abrupt contraction. This phenomenon is essentially equivalent to the phe nomenon that a slender body, namely a straight circular cylinder with a large length to diameter ratio, rotates towards a vertical orientation when falling through quiescent polymer solutions. Both shear thinning and elas ticity, thus, strongly contribute to the orientation process of fibers ; however, elasticity plays a dominant role. (2) The drastic change of the velocity field is due to viscoelasticity and flow rate in a channel with an abrupt contraction. The fiber orientation state, thus, is strongly influenced by these factors ; the fibers align in a manner of wine-glass shape as the contraction is approached, and the fiber orientation abruptly expands in the immediate downstream region of the contraction in a highly elastic fluid flow.

ビームスィープ・レーザスペックル写真法による定量的可視化法の開発

The speckle photography has been established as a method of velocity measurement in two-dimensional flow field at the same instance. This method is based on taking a double exposure photograph (specklegram) of measuring field, seeded with tracer particles and illuminated by pulsed light sheets. If a pulsed light source combined a low-power CW-laser with a beam chopper is used for this method, the intensity of light sheet is not sufficient to obtain a fine specklegram of the flow suspending with small tracer particles following up the flow.In this report, a new technique that the flow field is swept by a laser beam generated from a He-Ne laser source (15mW) is developed and named as the beam sweep laser speckle velocimetry. This method is applied to velocity measurement of a flow with a horseshoe vortex produced by a triangular column placed into a laminar boundary layer developed in a water channel flow suspending TiO2 particles (mean dia. 5μm). As the result, the fine specklegram is obtained for quantitative flow visualization.

Uveoscleral outflow using different-sized fluorescent tracers in normal and inflamed eyes

Sodium fluorescein and fluorescinated dextrans (FD) of selected molecular weights were combined and perfused into the anterior chamber of normal and inflamed eyes of cynomolgus monkeys. The eyes were dissected into iris, anterior and posterior uvea, anterior and posterior sclera, retina and intraocular fluids (excluding aqueous). Each tissue was homogenized and centrifuged and the supernatant was run through a gel-filtration column to separate the fluorescent tracers. Each of the resultant peaks was quantitated and facility of uveoscleral outflow was determined. In control eyes the calculated facility of uveoscleral outflow was very similar with all tracers (from 0.047-to 0.052 microliter min-1 mmHg-1) and each tracer was found in highest concentration in the anterior sclera and anterior uvea. In inflamed eyes the calculated facility of uveoscleral outflow increased two- to five-fold with each tracer (0.12-; 0.17-; 0.29-; and 0.24 microliter min-1 mmHg-1 with fluorescein, and the fluorescinated dextrans of MWs 4000, 40,000 and 150,000, respectively). Each tracer was found in the anterior sclera and uvea in inflamed eyes whereas the posterior sclera and uvea contained predominantly the higher molecular-weight tracers (MWs 40,000 and 150,000). It is concluded that iridocyclitis causes an increase in uveoscleral outflow by increasing the permeability of the anterior uvea to all tracers and fluid. Small tracers may then diffuse into uveal blood vessels or across the sclera, yielding lower values for uveoscleral outflow. Of the four tracers studied, the optimal tracer size for studying uveoscleral outflow in either normal or inflamed eyes is MW 40,000.

Capsaicin and blood-brain barrier permeability

The influence of perivascular sensory afferent nerve fibres upon the permeability of the blood-brain barrier was examined in halothane-anaesthetised rats. Blood-brain barrier permeability was assessed by the rate of transfer of the small neutral amino acid, [ 14C]α-aminoisobutyric acid, from blood to brain and by gross extravasation of Evans blue albumin. In every brain area examined, the acute administration of capsaicin (0.15–5 μmol/kg, i.v.) failed to alter significantly the passage into the brain of the small neutral amino acid tracer or to effect dye extravasation. Capsaicin, at concentrations which cause the release of vasoactive neuropeptides from nerve endings and increase vascular permeability in peripheral tissues, does not increase the permeability of the blood-brain barrier.

An experimental study of solute transport in a stony field soil

The transport of two conservative tracers, bromide and chloride, was studied in a stony field soil under natural soil, vegetative, and climatic conditions. Small tracer pulses were applied evenly over the 94‐m2 plot area in April 1982 (bromide) and October 1982 (chloride). A 15‐m‐long, 3‐m‐deep transect through the plot area was extensively sampled in May 1983, approximately 400 days after the bromide and 200 days after the chloride was applied. Tracer concentrations were obtained from 842 samples taken at 61 locations along the transect. Two‐dimensional contour plots of the data showed a relatively uniform displacement in the vertical direction, as well as a significant horizontal redistribution during the study period. The data were analyzed with the classical convection‐dispersion equation (CDE) and with a regional stochastic model that assumes logarithmic distributions of the pore water velocity and the dispersion coefficient across the field. Both models successfully described momentary field‐averaged concentration distributions but failed to predict observed concentration data in October 1984 when another, less intensive sampling was carried out. Pore water velocities could be estimated reasonably well with as few as five vertical sampling lines, whereas dispersion coefficients and solute loads required numerous additional samplings. A field scale dispersivity of about 8 cm was obtained for the CDE model. Between 75 and 130% of the applied tracers were recovered in 1982. The effects of sampling size (0.3 versus 3 kg dry soil weight) were found to be relatively small.

Retention of pinocytized solute by cho cell lysosomes correlates with molecular weight

We compared the exocytosis by Chinese hamster ovary (CHO) cells of a set of fluid-phase pinocytic tracers. The tracers were horseradish peroxidase (HRP), a glycoprotein of ~40 kDa, lucifer yellow (LuY), a 457 dalton, membrane-impermeant fluorescent dye, and glucose polymers ranging from sucrose through higher molecular weight, fluorescein isothiocyanate (FITC) dextrans. After a long term uptake (16–20 h), each of these tracers was localized to lysosomes. Exocytosis of the majority of the small molecule tracers, LuY and [ 14 C]sucrose, was observed over a period of a few to several h. There was no significant exocytosis of 42 kDa FITC dextran or HRP during an 18–20 h chase, while lower molecular weight dextrans were exocytosed. After co-accumulation of LuY and HRP in lysosomes, only the low molecular weight marker was exocytosed. These observations suggest retention of endocytized solutes within lysosomes is dependent on molecular size and may be limited by the rate of diffusion of molecules into shuttle vesicles.

Effects of Intravascular Contrast Media on Blood-Brain Barrier

The effects upon the rabbit blood-brain barrier after intracarotid injection of two non-ionic contrast media, iopentol (a monomer) and iodixanol (a dimer) were compared. Iothalamate and iohexol were used as reference substances. 99Tcm-DTPA, 125I-HSA and Trypsin blue were used as tracers in order to demonstrate various degrees of damage to the barrier. Injection of iothalamate led to large extravasation of 99Tcm-DTPA, 125I-HSA and Trypan blue which means severe damage of the blood-brain barrier. Injection of iopentol and iohexol resulted in some extravasation of all three tracers used, whereas injection of iodixanol only led to extravasation of the small molecule tracer 99Tcm-DTPA demonstrating minor changes of the barrier. At computed tomography of the brain with intravascular contrast medium enhancement it is safer to use iodixanol than iothalamate. Iodixanol is expected to cause even less adverse effects to the brain after intraarterial injection than iopentol and iohexol.

Afferents to the lateral reticular nucleus from the oculomotor region

By means of retrograde axonal transport of the wheat germ agglutinin-horseradish peroxidase complex, a projection from the Edinger-Westphal nucleus to the lateral reticular nucleus was demonstrated in the cat. Following small tracer ejections in the main part of the lateral reticular nucleus, a significant number of labelled neurons were found bilaterally throughout the Edinger-Westphal nucleus. Most of the labelled cells were located on the ipsilateral side. The projecting neurons are spindle-shaped to round with a maximum diameter of the cell body between 15 and 30 microns. The findings are discussed in relation to other Edinger-Westphal efferent projections, and some comments are made concerning the cytoarchitecture and delineation of the feline Edinger-Westphal nucleus.

Implantation of D-[3H]aspartate loaded gel particles permits restricted uptake sites for transmitter-selective axonal transport

Intracerebral pressure injections of small molecular tracers such as D-[3H]aspartate are usually followed by considerable spread which makes it difficult to assess the effective uptake area and precludes analysis of short axonal connections. As an attempt to circumvent these problems, D-[3H]aspartate was adsorbed onto gel beads that were subsequently packed into glass capillaries and implanted in the brain. Model experiments suggested that the loaded beads gradually release the tracer to the nerve tissue. The implantations resulted in small and sharply circumscribed tracer deposits which enabled us to study long axonal projections, as well as short intrahippocampal and intraamygdaloid pathways that are not easily resolved after pressure injections.

Plasma injection into a simulated magnetosphere

In an attempt to study the behavior of magnetospheric plasma, a laboratory “lerrella” experiment was performed using a plasma emitter which was a newly designed small discharge tracer called Powered Double Probe (PDP). The tracer plasma was observed optically along the magnetic field line which crosses the PDP position. The configuration of the magnetic field lines which are deformed by the plasma kinetic energy is one of the most important features of such a system. This paper deals with the usefulness of the PDP and an experimental study of this plasma injection into the simulated magnetosphere in the absence of the interplanetary magnetic field (IMF). By discharging the PDP a luminous plasma was observed along the magnetic field lines of a pure dipole field (without plasma flow) and a distorted dipole field (simulated magnetosphere) like a flash bulb converting a time exposure camera into a time resolved camera. From these observations it is deduced that a deformation of magnetic field line at the nightside region, in a sense of a decreasing magnetic field, is a result of interaction between a plasma flow and a dipole field, but no neutral sheet region exists in the simulated magnetosphere in the range of 30 earth radii for zero IMF. Also no notable oscillation or instability of the magnetic field lines in the simulated magnetosphere were observed. This supports the possible existence of “ground state” of the actual magnetosphere which was defined by a theoretical study of substorm mechanism.

Right and left cortical lesions asymmetrically alter cerebrovascular permeability in the rat

Vascular permeability and intravascular space in the rat cerebral cortex and hypothalamus were assessed 5 and 14 days after the production of either right or left hemisphere frontal cortical suction lesions. Rats were intravenously injected with large (dextran, 50,000 kdalton) and small (inulin, 5000 kdalton) molecular tracers and tissue samples were removed for assay after 7 min. Five days following lesions of the right but not left hemisphere, inulin levels in the cortical region posterior and contralateral to the lesion site were significantly higher than control values. Dextran levels were not increased in this region by lesions of either hemisphere. However, both right and left hemisphere lesions led to a significant elevation of inulin and dextran levels (inulin higher than dextran) in the cortex surrounding the lesion site. Fourteen days after lesion of either hemisphere, tracer levels were not elevated over control in any region examined. These results suggest that both right and left hemisphere cortical lesions transiently increase local vasopermeability (and perhaps intravascular space), but that only right hemisphere lesions selectively increase inulin in cortex distant from the lesion site, probably from lesion-induced alterations in cerebrovascular permeability.