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PubMed1982

Temporal and spatial distribution of fibronectin during development of the embryonic chick limb bud.

Indirect immunofluorescence has been used to study the distribution of fibronectin during the course of embryonic chick limb morphogenesis and differentiation. At all stages of development from 19 through 25, fibronectin is distributed throughout the non-differentiating mesenchymal tissue directly subjacent to the apical ectodermal ridge (AER), i.e. the mesenchyme extending 0.15 mm or so from the AER. Fibronectin is also distributed throughout the proximal condensing central core of the limb during the early stages of cartilage differentiation. In fact, fibronectin persists as a major component of the intercellular matrix in the central core of the limb following overt chondrogenic differentiation, since it is present as late as stage 27 throughout the well-differentiated cartilage rudiments of the radius, ulna, and humerus. The detection of fibronectin in differentiated cartilage is facilitated by pre-treatment of the sections with testicular hyaluronidase prior to immunofluorescent staining. In contrast to the chondrogenic central core of the limb, in the peripheral dorsal and ventral (myogenic) regions in which muscle differentiation is progressing, there is a progressive and striking diminution in fibronectin staining. By stage 27, little, if any, is present in the well-differentiated muscle primordia. Finally, at all stages of development, there is an accumulation of fibronectin at the ectodermal-mesenchymal interface, suggesting it is a component of embryonic limb basement membranes. On the basis of these observations, the possible role of fibronectin in limb cartilage and muscle differentiation and in other aspects of limb morphogenesis is discussed.

Age Factors↗
PubMed1980

The spatial distribution of polyribosomes in 3T3 cells and the associated assembly of proteins into the skeletal framework.

Acridine fluorescence reveals polyribosomes in fibroblasts and Triton-extracted skeletal frameworks; simultaneous phase-contrast images show cellular structure. Polyribosomes appear near nuclei of both intact fibroblasts and skeletal frameworks. Simultaneous autoradiography of cells so examined locates radioactive proteins. After synthesis, most proteins diffuse rapidly through the cytoplasm; intact cells autoradiographed afer a 35S pulse show grains throughout. In sharp contrast, extraction with Triton leaves only radioactive skeletal proteins, which, although released from ribosomes, are near polyribosomes after a pulse. After a chase, skeletal-associated radioactivity is found throughout the framework structure. However, skeletal proteins migrate only if protein synthesis continues. Emetine administered following a pulse block protein migration; skeletal framework radioactivity remains near polyribosomes. This also indicates limited exchange between skeletal framework and soluble cytoplasmic proteins. The fact that proteins insert themselves into the skeletal framework at or near their synthesis site, with limited subsequent exchange, appears to contradict current view of protein self-assembly.

Actins↗
PubMed1984

Spatial distribution of transcripts from the segmentation gene fushi tarazu during Drosophila embryonic development.

The locus fushi tarazu appears to be involved in the establishment of the segmentation pattern of the Drosophila embryo. The cuticle of ftz mutant embryos is missing structures in alternating segments such that only half the normal number of segments are present. We have localized ftz+ transcripts in tissue sections of wild-type Drosophila embryos by in situ hybridization. Transcripts from the ftz+ gene were first detected during nuclear cleavage prior to cell formation. During the last two nuclear divisions ftz+ transcription becomes gradually restricted such that at the cellular blastoderm stage the ftz+ transcripts are localized in seven evenly spaced bands of cells. The size of each band is similar to the size of the segment primordia at the blastoderm. By the time segmentation becomes morphologically distinct ftz+ transcripts are no longer detected. These results suggest that the ftz+ gene plays a key role in the determination of the segmentation pattern in the embryo.

Animals↗
PubMed1995

Spatial distribution and temporal change in cytosolic pH and [Ca2+] in resting and activated single human platelets.

In human platelets, a rapid rise in cytoplasmic Ca2+ and slower rise in cytoplasmic pH follow stimulation by thrombin. With the Ca2+ probe Fura-2 and the pH probe SNARF-1 for digitized fluorescence microscopy, we studied simultaneously the distribution and changes with time of [pH]i and [Ca2+]i in individual human platelets. In platelets coloaded with both probes, the probes had no detectable fluorescence at each other's excitation wavelength. The monovalent cation ionophore, nigericin (2 microM), produced a homogeneous rise in pH but no change in [Ca2+]. Platelets, in contact with glass, spread and developed an irregular, apparently mutually independent rise in both [Ca2+] and pH. Stimulation of platelets by thrombin 1.0 U/ml elevated [Ca2+]i and produced slow alkalinization without initial acidification. Replacement of extracellular Na+ by choline abolished thrombin-induced alkalinization, but had no effect on thrombin-induced [Ca2+]i elevation. ADP 10 microM caused a rapid rise of [Ca2+]i and transient alkalinization. Most stimulated platelets developed a gradient in pH, that was highest in the center. ADP and thrombin caused oscillation of [Ca2+]i but not of [pH]i. We conclude that alkalinization in stimulated platelets, presumably involving Na+/H+ antiport, is not essential for the rise of [Ca2+]i that may accompany it.

Adenosine Diphosphate↗
PubMed1981

A method for the study of the spatial distribution of the neuronal dendritic tree using a universal stage.

The use of a microscope equipped with a universal stage with 4 rotation axes, drawing tube and photographic system for the 3-dimensional study of neuronal morphology is considered. Two-dimensional projections of the neuronal tree are obtained by rotating the stage, and the application of coordinate transformations results in 3-dimensional mapping of neuronal topography. Algorithms used for these transformations are presented and the method applied to Golgi-impregnated neurons of the cerebral cortex of adult lizards. The advantages, limitations and sources of error of this method are discussed.

Animals↗
PubMed1994

The spatial distribution of pigeons' target detection.

Pigeons were trained to detect briefly-presented targets that appeared on a flatscreen computer display. Pecks were detected by a touchscreen mounted on the display. Those that were directed at the targets produced grain reward whereas pecks at locations in which the target had not appeared did not produce reward. A "behavioral fixation" procedure was used to ensure that the pigeons were facing the display when the target was presented. In general, the probability of detecting a target was highest in the region surrounding the fixation point and decreased as the target appeared more peripherally, both horizontally and vertically. These results show that pigeons' ability to detect targets in a frontal plane is not uniform.

Animals↗
PubMed1986

Simulation of the spatial distribution of muscle fibres in human muscles.

A composite muscle cross section model was simulated on a VAX 780 computer. The various motor unit territories in the cross section area were circular, partially overlapping each other. The radii of the territories of the motor units, their centres, and the number of muscle fibres in each motor unit were treated as random variables. Two different models were generated, one with a uniform distribution of the fibres in the motor unit territories, and the other with a normal distribution of the fibres. An algorithm for simulation of fibre density measurements was written, and the effects of varying the parameters of the model on fibre density measurements were investigated. The results of the computer simulation were in agreement with analytical and laboratory findings.

Computers↗
PubMed1996

Alzheimer's disease: preliminary study of spatial distribution at birth place.

Alzheimer's disease (AD) is a neurodegenerative disorder which is characterized by a progressive loss of memory and the alteration of cognitive functions. At least three chromosomal segments have been associated with early-onset AD in genetic linkage studies. These results argue for a certain degree of heterogeneity in the genetic origin of some forms of AD, although environmental risk factors cannot be ruled out in late-onset AD. In this preliminary study, we analyzed the geographical distribution of the birth places of a sample of 235 AD cases born in a defined region of Quebec (Canada), between 1895 and 1935. We wished to test the hypothesis that risk factors acting at, or around birth place and time play a role in the etiology of AD. The field of study was divided into rural and urban areas. A reference population of live births was used to compute a measure of odds ratio (OR). The OR results showed a statistically significant excess of AD cases in the rural area as compared to the reference population. When stratified for sex, the OR results showed a global excess of female AD cases in both the rural and the urban areas. For men, only the urban area presented a statistically significant deficit. We also analyzed the structures of the genealogical kinships of the rural and urban sub-groups. Although AD cases from the rural sub-group were more closely related to each other than those from the urban one, removal of the kin pairs from the OR analysis seemed to have little effect on the rural/urban distribution of cases. Therefore, the OR results would not appear to be due primarily to a difference in the kinship structures of the two sub-groups. This could mean that some risk factors for AD afflict women more strongly than men, the effect being different depending on the urban or rural origin. However, potential biases such as a higher rate of report for women, differential migration between birth places or a differential mortality ratio between sexes could produce spurious results in the direction of what we have observed in this preliminary study.

Aged↗
PubMed1990

Volume-dependent spatial distribution of microinjected thyrotropin-releasing hormone (TRH) into the medial preoptic nucleus of the rat: an autoradiographic study.

The present study was performed to quantify the distribution of a peptide neurotransmitter after microinjection into the medial preoptic area (POM), using a technique suitable for conscious animal preparations. The results indicate that only 50-nl volumes of injected tracer were sufficiently localized with 77 +/- 9% recovery in the POM. Injections of higher volumes resulted in an increasing spread of tracer into distant anatomical regions and structures, including the needle tract and cerebral ventricles. The amount of tracer localized in the POM decreased to 38 +/- 4% (200 nl) (P less than 0.05) and 14 +/- 8% (500 nl) (P less than 0.05), respectively. The data suggest that the volume of injection is critical for intraparenchymal injections into structures of a diameter of 1mm or less, such as the POM and should not exceed 50 nl in conscious animal preparations.

Animals↗
PubMed1989

Spatial distribution of pre- and postsynaptic sites of axon terminals in the dorsal horn of the frog spinal cord.

Axon terminals which could be interpreted as dorsal root boutons, were photographed from a series of 98 ultrathin sections with a Jeol 100B electron microscope. A total of 13 boutons were recovered for computer reconstruction. Two of them were terminal boutons, eight en passant boutons and three boutons were only partially recovered. All boutons contained multiple synaptic sites (maximum 33 and minimum seven) at which axodendritic and axoaxonic synapses were established. Axodendritic synapses were of the asymmetric type and they were directed toward adjacent dendrites. In axoaxonic synapses, which were of the symmetric type, the boutons were invariably on the postsynaptic side. Among the presynaptic profiles axons with spherical and pleomorphic vesicles and dendrites with flattened vesicles could be discerned. On average, each 2.67-microns2 bouton surface area contained one presynaptic site at which an axodendritic synapse was established, and each 7-microns2 surface area contained one postsynaptic site for an axoaxonic (or dendroaxonic) contact. A tendency of grouping of synaptic sites was observed. Distance measurements between the closest neighbours of all synaptic sites were made in four combinations in boutons with the original and with a random distribution of synaptic sites. The arithmetic mean of distances measured between the presynaptic and the closest postsynaptic sites was almost twice as big as that measured in the reverse direction. The difference between these values became greatly reduced in the case of random distribution. The arithmetic mean of distances between the closest neighbours of presynaptic sites was about the same as that between the closest neighbours of postsynaptic sites. This latter value was considerably increased with randomly distributed synaptic sites. The results suggest a non-random distribution of synaptic sites on the surface of boutons. The analysis of cluster formation of synaptic sites performed with a numerical taxonomy technique revealed that the majority of the 153 synaptic sites were comprised in 27 clusters containing both pre- and postsynaptic sites within the 1-micron similarity level. All postsynaptic sites were within 1 micron of one or more presynaptic sites. On the basis of the assumption that the postsynaptic sites are occupied by inhibitory axoaxonic synapses, it is suggested that the transmitter release from the presynaptic sites can be individually controlled in this structural arrangement. A probable mechanism of this function may be the passive invasion of the bouton by the impulse propagating actively along the dorsal root fibre.

Animals↗
PubMed1989

Functional organization of the medial division of the medial geniculate body of the cat: tonotopic organization, spatial distribution of response properties and cortical connections.

The discharge properties of 735 single units located in the pars magnocellularis (M) of the medial division of the medial geniculate body (MGB) were studied in 23 nitrous oxide anesthetized cats in response to simple acoustic stimuli (clicks, noise and tone bursts). A systematic decrease of single unit characteristic frequencies (CF) was observed along electrode track portions crossing M from dorso-medial to ventro-lateral. These data indicate that M is tonotopically organized with an arrangement of low CF units latero-ventrally and high CF units dorso-medially. This preferential arrangement of single units as a function of their CF was consistent with the location and orientation of clusters of labeled cells in M resulting from wheat-germ agglutinin labeled with horseradish peroxidase (WGA-HRP) injections in CF defined loci in the anterior (AAF) or primary (AI) auditory cortical fields. The quality of the tonotopic arrangement was low caudally and increased in the rostral direction, indicating that this tonotopicity concerns mainly the anterior half of M. Response latencies to clicks, noise and tone bursts were on average longer in the posterior part of M than in its anterior part. Time-locking of discharges in response to repetitive acoustic pulses was more frequent anteriorly than posteriorly and the upper limiting rate of locking was on average higher rostrally (up to 200-300 Hz). In contrast, other response properties such as responsiveness to the various combinations of simple acoustic stimuli, response patterns and tuning were more randomly distributed in M, showing the whole range of response properties seen in the MGB. Data derived from several injections of WGA-HRP performed in distinct auditory cortical fields in several animals indicated that M projects to the tonotopic cortical fields (AAF, AI and PAF) as well as to the non-tonotopically organized secondary auditory cortex (AII). The contribution of M to the total thalamic input reaching each field of the auditory cortex was quantitatively more important for AAF (30%) and PAF (20%) than for AI and AII (about 10% each).

Acoustic Stimulation↗
PubMed1989

Spatial distribution of glutamate, taurine and GABA in teleosts and mammals retina: in vivo and in vitro study.

Teleost and amphibian retina grows throughout life at the circumferential margin distal to the center. Retinas of two teleosts, goldfish and Eugerres plumieri; and two mammals, rat and rabbit were dissected into concentric regions; center and periphery; or center, intermediate and periphery. The concentration of glutamic acid, taurine, and gamma-aminobutyric acid was determined in these areas. A non-significant difference was found between the center and periphery of retinas dissected into two regions. By dissecting the teleost retina in three concentric regions a progressive increase of gamma-aminobutyric acid and taurine for center to periphery was observed, which was statistically significant for taurine. Rat and rabbit retina did not present this difference. The concentration of these amino acids was also determined in two concentric regions of goldfish retina 24 hr after crush of the optic nerve. Taurine content significantly increased in the center of the regenerating retina, but not in the periphery. Outgrowth was measured in explants prepared from central and peripheral retina in the presence of exogenous taurine. The amino acid produced an increase of the nerve growth index of central explants, but inhibited the growth from peripheral explants. This report presents a correlation between taurine concentration in a region of the retina that could be considered as embryonic tissue, suggesting that this amino acid plays a role in the formation of new cells. Moreover, the results from post-crush and cultured retina, with respect to taurine concentration or regenerating effect, suggest a saturation of the taurine-enriched zone.

Animals↗