Lateral diffusion in an archipelago. The effect of mobile obstacles.

Lateral diffusion of mobile proteins and lipids (tracers) in a membrane is hindered by the presence of proteins (obstacles) in the membrane. If the obstacles are immobile, their effect may be described by percolation theory, which states that the long-range diffusion constant of the tracers goes to zero when the area fraction of obstacles is greater than the percolation threshold. If the obstacles are themselves mobile, the diffusion constant of the tracers depends on the area fraction of obstacles and the relative jump rate of tracers and obstacles. This paper presents Monte Carlo calculations of diffusion constants on square and triangular lattices as a function of the concentration of obstacles and the relative jump rate. The diffusion constant for particles of various sizes is also obtained. Calculated values of the concentration-dependent diffusion constant are compared with observed values for gramicidin and bacteriorhodopsin. The effect of the proteins as inert obstacles is significant, but other factors, such as protein-protein interactions and perturbation of lipid viscosity by proteins, are of comparable importance. Potential applications include the diffusion of proteins at high concentrations (such as rhodopsin in rod outer segments), the modulation of diffusion by release of membrane proteins from cytoskeletal attachment, and the diffusion of mobile redox carriers in mitochondria, chloroplasts, and endoplasmic reticulum.     

Different vascular permeability between the sensory and secretory circumventricular organs of adult mouse brain

The blood-brain barrier (BBB) prevents free access of circulating molecules to the brain and maintains a specialized brain environment to protect the brain from blood-derived bioactive and toxic molecules; however, the circumventricular organs (CVOs) have fenestrated vasculature. The fenestrated vasculature in the sensory CVOs, including the organum vasculosum of lamina terminalis (OVLT), subfornical organ (SFO) and area postrema (AP), allows neurons and astrocytes to sense a variety of plasma molecules and convey their information into other brain regions and the vasculature in the secretory CVOs, including median eminence (ME) and neurohypophysis (NH), permits neuronal terminals to secrete many peptides into the blood stream. The present study showed that vascular permeability of low-molecular-mass tracers such as fluorescein isothiocyanate (FITC) and Evans Blue was higher in the secretory CVOs and kidney as compared with that in the sensory CVOs. On the other hand, vascular permeability of high-molecular-mass tracers such as FITC-labeled bovine serum albumin and Dextran 70,000 was lower in the CVOs as compared with that in the kidney. Prominent vascular permeability of low- and high-molecular-mass tracers was also observed in the arcuate nucleus. These data demonstrate that vascular permeability for low-molecular-mass molecules is higher in the secretory CVOs as compared with that in the sensory CVOs, possibly for large secretion of peptides to the blood stream. Moreover, vascular permeability for high-molecular-mass tracers in the CVOs is smaller than that of the kidney, indicating that the CVOs are not totally without a BBB.     

The gastric mucosal barrier: structure of intercellular junctions in the dog

The canine gastric mucosa consists of two regions, the surface mucous cells and gland area cells including parietal, chief, and mucous-containing cells. We have used quantitative freeze-fracture methods in conjunction with thin-section extracellular tracers to document and correlate tight junction morphology with epithelial permeability. The number of strands in the tight junction complexes of the surface cells and gland cells is the same, but differences in strand arrangement exist. The surface cells have an interwoven tight junction configuration which is impermeable to extracellular tracers. The gland cell junctions are regularly arranged and often permeable to extracellular lanthanum. The possibility that the observed difference in permeability between the tight junctions of the surface mucous cells and those of the gland cells is related to their structural configuration is discussed.     

Projections of Olfactory Bulbs and Non-Olfactory Telencephalic Structures in Amygdaloid Complex of the Turtle <Emphasis Type="Italic">Testudo horsfieldi</Emphasis>: A Study Using Anterograde Tracer Technique

To confirm the discrete character of projections of telencephalic olfactory and non-olfactory structures to the amygdaloid complex (AC) in the terrestrial turtle Testudo horsfieldi, a study was performed by the method of anterograde axonal transport of tracers (HRP, BDA). After a massive injection of the tracers into the main and accessory olfactory bulb, a dense accumulation of labeled fibers and terminals was found in ventral part of AC in the neuropil zones of nbam (J) and ncoam and very scanty—in nmam and ncam. After a massive injection of the tracers into non-olfactory telencephalic structures including dorsal cortex, pallidal enlargement, and ADVR, a very dense terminal field was observed in the dorsal AC part and a less dense one, with predominance of labeled fibers, in its ventral part. Local administration of the tracers separately into the dorsolateral (visual area) and the ventromedial (auditory-somatic area) parts of the ADVR allowed revealing discrete projections, respectively, to the laterocentral and mediocentral areas of the dorsal AC part with a relative overlapping in the central AC area. In all experiments, retrogradely labeled neurons in AC were also observed in zones of the corresponding bulbar and rostrotelencephalic projections. Thus, it has been shown that in the turtle AC there exist not only separation of direct olfactory and non-olfactory projections, but also discrete projections of different sensory areas of ADVR. Reciprocity of these connections is also confirmed. Organization of afferent olfactory and non-olfactory telencephalic connections in AC is similar in reptiles and in mammals.     

Chesapeake Bay nutrient budgets — a reassessment

Recently published annual mass balances or budgets for nitrogen, phosphorus, and silicon in Chesapeake Bay have pictured the estuary as retaining a very large fraction, perhaps all, of the nutrients that enter from land drainage, the atmosphere, and anthropogenic discharges. However, these budgets have been based on estimates of the net exchanges of nutrients at the mouth of the bay or on the rates of accumulation of nutrients and sediments calculated from the distributions of various geochemical tracers in the sediments. While conceptually straightforward, the first approach is subject to large errors because it requires the determination of a small "signal" against a large background of tidal "noise". The second approach has led to overestimates of the nutrient trapping efficiency of the bay because tracer-derived sediment deposition rates have been multiplied by the surface area of the whole bay or various parts of the bay rather than by the smaller area of active sediment deposition. This approach is also incorrect because the average, long-term rates of sediment deposition measured by the geochemical tracers, including major floods, have been compared to shorter-term records of nutrient input.The more appropriate calculation of nutrient retention based on contemporaneous measurements of nutrient and sediment input and the chemical compositon of sediments accumulated in the estuary shows that Chesapeake Bay retains only some 3–6% of the nitrogen, 11–17% of the phosphorus and 33–83% of the silicon brought into its waters during a year in which no major flood occurred.This behavior suggests that current problems of estuarine eutrophication are more a consequence of present nutrient inputs than an inevitable or inescapable legacy of past enrichment. It also follows that the management or manipulation of nutrient loadings to esturies may lead to a more rapid response in environmental quality than previously predicted.     

Organization of the direct projections of the Tsai ventral tegmental area to the hippocampus

In this report we have examined the distribution in the ventral tegmental area of Tsai (VTA-A10) of the neurons projecting to the hippocampal formation (HF) by injecting, in different combinations, retrograde fluorescent tracers (Fast Blue, 2% and Nuclear Yellow, 1%) in several hippocampal areas. The distribution of the VTA labeled neurons suggest a topographic organization of the VTA efferent pathway towards the HF. These results are in agreement with the concept that precise topography of the projections is a distinctive feature of the dopaminergic systems in general.     

Topography of the rat blood-testis barrier after intratubular administration of intercellular tracers

Intratubular injection of electron-opaque tracers (lanthanum hydroxide, peroxidase) by micromanipulation showed that the intercellular spaces of the adluminal compartment are in continuity with the lumen of the rat seminiferous tubule at all stages of the spermatogenic cycle. This continuity involves the intercellular spaces which surround zygotene spermatocytes and late leptotene spermatocytes in stages X-XI. The present observations would seem to cast doubt on the real existence of a third compartment, or intermediate compartment, in the seminiferous epithelium. In the material which, in addition to intratubular administration, had been treated with intravascular tracer perfusion, we found the presence of a parabasal region of interSertoli junctions where the tracer stopped whatever its direction. Freeze-fracture replicas exhibit interSertoli tight junctions arranged, from basal lamina to lumen, in three well-defined patterns: in the most basal area, which is the zone of free penetration of tracers from the peritubular environment, junctions are very sparse or absent; a belt of closely apposed continuous and parallel junctions, also parallel to the basal lamina, is the exclusion zone which prevents tracer penetration from either direction; the most apical membrane areas display irregularly arranged, loosely spaced and frequently interrupted rows of particles, most tending to be perpendicular to the basal lamina. This area corresponds to the territory where the intraluminally injected tracer permeates the interSertoli space.     

Steady-state methods for the study of placental exchange.

Published and new data on steady-state exchange of tracers and oxygen are characterized by marked species differences. When the placenta is treated as an ideal diffusion cell of unknown vessel geometry and permeability, the exchange characteristics of oxygen can be used to prove that the exchange of tracers such as acetylene, nitrous oxide, tritiated water and antipyrine is entirely flow limited. The recorded patterns of transfer of flow-limited tracers reveal that some placentas are as effective as counter-current exchangers whereas others mimic the behavior of the less effective types of exchangers. These species differences in apparent geometry are unrelated to the histologic nature of the barrier. The patterns of flow-limited transfer are so similar to those of oxygen transfer that the diffusion resistance to oxygen must be small. The exchange of diffusion-limited (hydrophilic) tracers mimics exchange across capillary membranes in some species and exchange across cell membranes in others. These species differences in diffusion-limited transfer are clearly related to the histologic nature of the barrier and are independent of vessel geometry.     

Efferent projections from the retrochiasmatic area to the median eminence and to the pars nervosa of the hypophysis with special reference to the A15 dopaminergic cell group in the sheep

Anterograde tracers, viz. Phaseolus vulgaris leucoagglutinin and fluorescein dextran, were used in conjunction with tyrosine hydroxylase immunohisto-chemistry to study the projections of the A15 dopaminergic cell group towards the median eminence and pituitary in sheep. After injection of the tracers in the retrochiasmatic area, which contains the cell group A15, fibres containing anterograde tracer were observed in the internal zone of the median eminence and in the pars nervosa of the pituitary. Numerous tyrosine hydroxylase immunoreactive fibers were present in the external zone of the median eminence and in the pars intermedia and the pars nervosa of the pituitary, with characteristic patterns of organisation in each area. Most tyrosine hydroxylase-immunoreactive fibres containing fluorescein dextran were located in the pars nervosa, whereas only a few were observed in the internal zone of the median eminence. It was concluded that at least part of the dopaminergic innervation of the pars nervosa originated from the A15 group. These results provide morphological evidence for (1) the role of dopaminergic neurons of the A15 cell group in the seasonal control of prolactin secretion via the release of dopamine in the pars nervosa, and (2) putative physiological interactions between dopamine and the secretion of neurohypophysial hormones in sheep.     

Evaluation of biotracers to monitor effluent retention time in constructed wetlands

AIMS: With concern surrounding the environmental impact of chemical tracers on the aquatic environment, this paper presents the initial evaluation of biotracers used to determine the effluent retention time, an important performance indicator, in a Free Water Surface Constructed Wetland. METHODS AND RESULTS: Production of the biotracers, coliphage MS2, and the bacteriophage of Enterobacter cloacae and antibiotic resistant endospores of Bacillus globigii is described in detail. Their subsequent use in three separate tracer experiments - January, March and June (2000) - revealed the variability of retention time with respect to effluent flow. The biotracer MS2 showed the constructed wetland had a retention time of 8-9 h at a mean discharge of 0.9 l s-1, increasing to 10-12 h at a mean discharge 0.3 l s-1. A similar retention of 9-10 h at a mean discharge of 0.3 l s-1 was calculated for the Ent. cloacae phage. In contrast, use of endospores revealed considerably longer retention times at these mean discharge rates; 12-24 h and 36-48 h, respectively. CONCLUSION: Biotracers could provide a useful and environmentally friendly technique to monitor effluent retention in constructed wetlands. At this stage the phage tracers appear particularly promising due to ease of isolation and recovery. SIGNIFICANCE AND IMPACT OF THE STUDY: Initial results are encouraging and have highlighted the potential of biotracers as alternatives to chemical tracers, even in microbially-rich waters.     

The organization of corticocortical projections from area 17 to area 18 of the cat's visual cortex

Retrogradely transported tracers were injected into area 18 of the visual cortex of the adult cat to study the organization of corticocortical projections from area 17 to area 18. All injections, whether very small or relatively large, and irrespective of their exact location in area 18, produced a discontinuous, clustered distribution of labelled cells, mainly in layers II, III and upper IV, in a topographically related region of area 17. The mean centre-centre distance between neighbouring patches was about 750 microns. We conclude that the overall population of cells projecting to area 18 is genuinely distributed in a patchy fashion and that they provide an efficient spatial sample of information from area 17. Comparison of the dimensions of each injection site and of the retrogradely labelled territory suggested that each region in area 18 receives a convergent input from a zone in area 17 whose visual field representation is about 0.8 M-1 deg larger in all directions (where M is the magnification factor in millimetres per degree at the termination site in area 18). Pairs of injection were made in area 18 by placing small volumes of two fluorescent tracers, fast blue and diamidino yellow, side-by-side in either a rostrocaudal or a mediolateral plane, with different distances between them. When the boundaries of the dense central cores of two injection sites were separated, at their closest points, by about 1.6 mm, the two corresponding distributions of labelled cells in area 17 were just non-overlapping, suggesting that each group of cells in area 17 sends a divergent projection in innervate a zone about 0.8 mm larger in all directions in area 18. More closely spaced injections led to overlap of the distributions of labelling by the two dyes, with shared clusters containing a mixture of labelled cells. The proportion of double-labelled cells in these shared clusters never exceeded 4.4% (but was 70% after sequential injection of the two dyes at a single point). We conclude that, although each cluster of cells sends a divergent projection to area 18, the majority of individual axons terminate more discretely, perhaps providing specific inter-connections between functionally corresponding 'columns' in the two areas.     

水汽来源和环境因子对湖南会同大气降水氢氧同位素组成的影响

氘(D)和¹⁸O是水中常见的环境示踪剂,研究大气降水氢氧稳定同位素组成是研究区域及全球水循环过程的必要前提。为了揭示降水同位素组成对环境因子的响应机制,本研究在中国科学院会同森林生态实验站收集了2017年5月—2019年8月149次不同量级大气降水样品及环境因子数据,分析该地区大气降水氢氧同位素的时间变化特征,探讨水汽来源和环境因素对降水氢氧稳定同位素组成的影响。结果表明: 湖南会同大气降水线方程为: δD=(7.45±0.17)δ¹⁸O+(10.10±1.25) (R²=0.93,P<0.01),斜率比中国及全球大气降水线斜率略低;大气降水中稳定同位素组成与局地环境因子密切相关,并对季风气候中的水汽来源响应敏感,表现为夏季风期间¹⁸O和D贫化,冬季风期间¹⁸O和D富集;夏季风期间,受到孟加拉湾、南海和西太平洋在夏季风和季风后3种不同气压下远距离海洋水汽的影响,过量氘均值接近全球平均值;冬季风期间,大气降水氢氧同位素值受到远距离西风气团、孟加拉湾退化热带海洋气团、季风前期内陆水汽和局地环境因子的共同作用,大气降水线斜率偏低,过量氘值偏大。     

Renal excretion of methylene-diphosphate-technium-99m. Preliminary observations

The purpose of this study is to elucidate the mechanism of the renal excretion of 99mTc-MDP in man. We compared the renal clearance of 99mTc-MDP and 51Cr-EDTA (glomerular filtration rate agent). Since the 99mTc-MDP is bound to the plasma protein, the free fraction was calculated by dialysis. The clearances were obtained by single-injection technique. The plasma disappearance of the tracers was resolved into three exponential functions and area was calculated. The clearance was calculated by dividing the amount of the tracers excreted during the first four hours and the plasma area. In this study no difference was found in the clearance of the two agents. These findings suggest that the renal excretion of diphosphonate is related to the glomerular filtration rate.     

The use of neutron activation analysis in pollination ecology

Neutron activation analysis in pollination ecology was examined with particular regard to external application of indicator elements. Movement of elements between flowers can be detected after external application either to the anthers or, in members of the Asteraceae, to the entire head. This technique is potentially useful in studying pollen flow within and between populations and in detecting flower constancy of pollinators. This technique is advantageous when compared with the use of radioactive tracers because potential health and environmental hazards inherent in the field use of unstable isotopes are eliminated.     

Synthesis of CpFe(CO)(L) complexes of hydantoin anions (Cp = eta5-C5H5, L = CO, PPh3), and the use of the 5,5-diphenylhydantoin anion complexes as tracers in the nonisotopic immunoassay CMIA of this antiepileptic drug.

As part of our ongoing development of the CMIA nonisotopic immunoassay method, in which the tracers are metal carbonyl complexes and detection is by Fourier transform infrared spectroscopy, we examined the potential use as tracers of the complexes CpFe(CO)2(5,5-diphenylhydantoin) 2d and CpFe(CO)(PPh3)(5, 5-diphenylhydantoin) 3. The present study involved the synthesis of a series of hydantoin complexes (2a-2d), in particular that of the derivative of 5,5-diphenylhydantoin 2d. The structure of 2d was confirmed by X-ray crystallography. The infrared analysis, establishing the position and intensity of the characteristic metal-carbonyl peaks of complexes 2d and 3 in the 1850-2200 cm-1 region, shows that measurement of the absorbance values of these characteristic peaks will permit quantitative analysis in the picomole range, the norm for routine use in immunoassay and thus suitable for use as CMIA tracers. Cross-reaction rates of these tracers with anti-DPH specific antibodies show that 2d and 3 are both recognized by anti-DPH antibodies (cross-reaction rates 43 and 20%, respectively). In developing a CMIA of DPH with these tracers, it was found that 3, with a single, intense band at 1977 cm-1, had very promising IR characteristics for use in multiassay CMIA, but probably owing to its relatively weak affinity for the antibodies, it was not possible to develop a CMIA for DPH using this tracer. Complex 2d, however, showed better recognition by the antibodies, and using this complex as a tracer, it was possible to develop a particularly sensitive monoassay of DPH by the CMIA method.     

Wind tunnel evaluation of several tracer and collection techniques for the measurement of spray drift

In the history of pesticide drift measuring techniques, different tracers and a lot of different collection techniques have been used. At the start of a new Flemish project 'Protecting the Flemish environment against drift - The importance of drift-reducing techniques', wind tunnel tests have been executed to select the most efficient tracer and collection technique. As tracer types a fluorescent tracer Renaissance W15, 2 different chelates, a NaCl-solution and a fungicide Tolylfluanide were used. 2 different collection techniques were tested: drains incorporated in the wind tunnel floor filled with filter paper and filled with cloths. The recovery of the different tracers combined with the 2 collection materials was calculated. The advantages and disadvantages of the tracers and collection materials are enumerated in this article.     

Drainage of the prelymphatics of the brain via the adventitia of the vertebral artery

Carbon particles injected into the cortex of the cerebellum of the rat were found in the Virchow-Robin spaces of the adjacent capillaries, and in the adventitia of the cerebellar artery, basilar artery and vertebral artery--both inside and outside the skull. They were also found in some portions of the deeper cervical lymph nodes. However, while tracers injected into the cerebral hemispheres are drained via the tissue channels in the adventitia of the internal carotid arteries, tracers injected into the cerebellar hemispheres are drained via those of the vertebral arteries.     

An examination of somatosensory area SIII in ferret cortex

A somatotopically organized region on the suprasylvian gyrus of the ferret was examined using multiunit recordings and anatomical tracer injections. This area, which contains a representation of the face, was bordered by the primary somatosensory area (SI), anteriorly, and by the visually responsive rostral posterior parietal cortex (PPr), posteriorly. Anatomical tracers revealed connections to this region from cortical areas MI, SI, MRSS, PPr, and the thalamic posterior nucleus. These results are consistent with previous work in ferrets as well as with the location, physiology, and connectivity of area SIII in cats. Given its associations, functional properties, location, and homology, it is proposed that this region represents the third cortical somatosensory area (SIII) in ferrets.     

Visible light-dependent degradation of lipidic phytoplanktonic components during senescence: a review

Though most of the organic components of phytoplankton are susceptible to being photodegraded during senescence, until recent years there has been very little research in this area. Recently, however, there have been a renewal of interest, and the heterogeneous visible light-induced degradative reactions of lipidic compounds associated with phytodetritus have been studied. The present paper reviews the results obtained in the course of these studies. In the first part, the production and quenching of excited states of chlorophyll and toxic oxygen species (singlet oxygen, superoxide ion, hydroxyl radical and hydrogen peroxide) in healthy and senescent phytoplanktonic cells are discussed. Then, the photo-oxidation of the main lipidic cell components (chlorophyll, chlorophyll phytyl chain, carotenoids, sterols, unsaturated fatty acids, alkenones and unsaturated alkenes) in senescent phytoplanktonic cells is examined. Emphasis is given to the degradation rates and the mechanisms of visible light-induced degradation of the main lipidic components of phytoplankton and to the structure of the photoproducts formed. In each case, the selectivity of these compounds is discussed in order to select a "pool" of photoproducts able to act as tracers of photo-oxidative alterations in the marine medium. This "pool" of photoproducts could provide very useful information concerning the physiological state of phytoplanktonic communities and current environmental problems related to ozone depletion.     

Topography of the thalamo-cortical projections on trunk representation demonstrated by fluorescent neuro-tracers

With the aim to study the detailed topography of the thalamo-cortical neurones projecting to the trunk representation zone of the first somatosensory area (SI), punctate injections of three different fluorescent tracers (Evans Blue, Nuclear Yellow and Fast Blue) were performed in the three physiologically defined subareas forming the trunk region of SI. These injections resulted in the labelling of three different cell aggregates, narrow in dorsoventral and mediolateral extent but elongated rostrocaudally, located in topographically distinct regions of the nucleus ventralis posterio-lateralis. The results suggest that the highly organized topography of the trunk representation of area SI is imposed by the thalamo-cortical input from VPL.