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  • Articles  (24)
  • 1990-1994  (22)
  • 1905-1909
  • Medicine  (24)
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  • Articles  (24)
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  • 1
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    Maize regulatory gene opaque-2 encodes a protein with a "leucine-zipper" motif that binds to zein DNA. (1990)
    National Academy of Sciences
    Details
    Publication Date: 1990-01-01
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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    PAPER CURRENT
  • 2
    Electronic Resource
    Electronic Resource
    Isolation of motile and non-motile insertional mutants of Campylobacter jejuni: the role of motility in adherence and invasion of eukaryotic cells (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 14 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A method of insertional mutagenesis for naturally transformable organisms has been adapted from Haemophilus influenzae and applied to the study of the pathogenesis of Campylobacter jejuni. A series of kanamycin-resistant Insertional mutants of C. jejuni 81–176 has been generated and screened for loss of ability to invade INT407 cells. Eight noninvasive mutants were identified which showed 18-200-fold reductions in the level of invasion compared with the parent. Three of these eight show defects in motility, and five are fully motile. The three mutants with motility defects were further characterized to evaluate the method. One mutant, K2–32, which is non-adherent and non-invasive, has an insertion of the kanamycin-resistance cassette into the flaA flagellin gene and has greatly reduced motility and a truncated flagellar filament typical of flaA mutants. The adherent non-invasive mutants K2–37 and K2–55 are phenotypically paralysed, i.e. they have a full-length flagellar filament but are non-motile. All three mutants show an aberration in flagellar structure at the point at which the filament attaches to the cell. Mutants K2–37 and K2–55 represent overlapping deletions affecting the same gene, termed pflA (paralysed flagella). This gene encodes a predicted protein of 788 amino acid residues and a molecular weight of 90 977 with no significant homology to known proteins. Site-specific insertional mutants into this open reading frame result in the same paralysed flagellar phenotype and the same invasion defects as the original mutants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb01324.x
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  • 3
    Electronic Resource
    Electronic Resource
    Lead exposure from conventional and cottage lead smelting in Jamaica (1991)
    Springer
    Archives of environmental contamination and toxicology 21 (1991), S. 65-71 
    Details
    ISSN: 1432-0703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Notes: Abstract A survey was conducted to determine the distribution and determinants of environmental and blood lead levels near a conventional and several cottage lead smelters and to assess the relationship between environmental and blood lead levels in a tropical, developing-country setting. Fifty-eight households were studied in the Red Pond community, the site of the established smelter and several backyard smelters, and 21 households were studied in the adjacent, upwind Ebony Vale community in Saint Catherine Parish, Jamaica. Households were investigated, using questionnaires, soil and housedust lead measurements, and blood lead (PbB) measurements from 372 residents. Soil lead levels in Red Pond exceeded 500 parts per million (ppm) at 24% of households (maximum-18,600 ppm), compared to 0% in Ebony Vale (maximum 150 ppm). Geometric mean PbB in Red Pond, where 44% of children 〈6 years of age had PbB levels ≥ 25 micrograms per deciliter (μg/dL), was more than twice that Ebony Vale in all age groups (p 〈 0.0005). Within Red Pond, proximity to backyard smelters and to the conventional smelter were independent predictors of soil lead (p 〈 0.05). Soil lead was the strongest predictor of PbB among Red Pond subjects under 12 years of age. The blood lead-soil lead relationship in children differed from that reported in developed countries; blood lead levels were higher than expected for the household-specific soil lead levels that were observed. These data indicate that cottage lead smelters, like conventional ones, are a hazard for nearby residents and that children exposed to lead contamination in tropical, developing countries may be at higher risk for developing elevated blood lead levels than similarly-exposed children in developed countries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01055558
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  • 4
    Electronic Resource
    Electronic Resource
    Selective suppression of the magnocellular visual pathway during saccadic eye movements (1994)
    [s.l.] : Nature Publishing Group
    Nature 371 (1994), S. 511-513 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We measured contrast sensitivity to horizontal gratings of various spatial frequencies, briefly presented during large voluntary horizontal saccades. As the saccades ran parallel to the bars of the gratings, they produced no effective image motion. The gratings were modulated sinusoidally either in ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/371511a0
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  • 5
    Electronic Resource
    Electronic Resource
    Italian university structure (1992)
    [s.l.] : Nature Publishing Group
    Nature 357 (1992), S. 273-273 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - Many readers not familiar with the structure of Italian universities may be confused by the recent controversy aired in these columns1"5. As a foreigner (Australian) with several years experience of Italian academic life, I am perhaps well placed to try to explain some of the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/357273a0
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  • 6
    Electronic Resource
    Electronic Resource
    Contribution of collagen and mineral to the elastic anisotropy of bone (1994)
    Springer
    Calcified tissue international 55 (1994), S. 381-386 
    Details
    ISSN: 1432-0827
    Keywords: Acoustic microscopy ; Bone ; Collagen fiber ; Elastic anisotropy ; Mineral crystal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract It has long been thought that collagen fibers within the bone matrix are deposited in an aligned pattern that channels mineral growth. If this model of bone structure is correct, both organic and inorganic phases of bone should have similar elastic anisotropy. Using an acoustic microscope, we measured longitudinal and transverse acoustic velocities of cortical specimens taken from 10 dog femurs before and after removal of either the mineral (using 10% EDTA) or collagen phases (using 7% sodium hypochlorite) and calculated longitudinal (CL) and transverse (CT) elastic coefficients. The anisotropy ratio (CL/CT) decreased significantly after demineralization (1.61 before versus 1.06 after, P〈0.0001, paired t-test). However, there was no significant change after decollagenization (1.51 before versus 1.48 after, P=0.617, paired t-test). We conclude that the orientation of mineral crystals is the primary determinant of bone anisotropy, and the collagen matrix within osteonal bone has little directional orientation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00299319
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  • 7
    Electronic Resource
    Electronic Resource
    Remodeling and the repair of fatigue damage (1993)
    Springer
    Calcified tissue international 53 (1993), S. S75 
    Details
    ISSN: 1432-0827
    Keywords: Microdamage ; Remodeling ; Fatigue ; Osteoporosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary This paper reviews the direct and indirect evidence for and against the idea that bone remodeling repairs fatigue damage. It defines experiments that should be performed to determine whether the accumulation and repair of fatigue damage is relevant to the pathogenesis of osteoporotic fracture. The experimental evidence favors the hypothesis that microdamage evokes local remodeling. The data suggest that the balance between the microdamage burden and bone repair is nearly constant. The indirect evidence comes from clinical observations that show positive relationships between depressed bone formation rate or prolonged remodeling period with bone fracture. More compelling indirect evidence comes from studies in which bone remodeling was pharmaceutically depressed, and fracture incidence rose in direct proportion. Data on microdamage accumulation were not collected in these studies. Conversely, some experimental evidence disputes a direct relationship between fatigue microdamage and repair. In these studies, increased amounts of bone microdamage in hyperadrenocortical dogs, and in irradiated dogs, could not be demonstrated even though bone fragility increased without associated osteopenia. Finally, the indirect evidence that argues that microdamage does not initiate repair is based on inference and does not provide an adequate test of the hypothesis. In balance, the current body of evidence favors the contention that bone remodeling repairs fatigue damage and thereby prevents fracture. Future studies should verify that microdamage accumulates when bone fracture occurs in conjunction with depressed remodeling activation frequency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01673407
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  • 8
    Electronic Resource
    Electronic Resource
    Scanning motion, ocellar morphology and orientation mechanisms in the phototaxis of the nematode Mermis nigrescens (1990)
    Springer
    Journal of comparative physiology 167 (1990), S. 257-268 
    Details
    ISSN: 1432-1351
    Keywords: Scanning motion ; Shadowing ; Ocellus ; Mechanism ; Orientation ; Phototaxis ; Klinotaxis ; Photomovement ; Transverse phototaxis ; Nematode
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The putative ocellus of Mermis females consists of a hollow cylinder of dense hemoglobin pigmentation located in the anterior tip. The exact location of the photoreceptive nerve endings, however, is unknown. During phototaxis a continual bending or scanning motion of the head (anterior 2 mm) causes the orientation of the tip to swing about the direction of the source. By turning off (shuttering) the light source whenever the tip orientation was to one side of the source direction, the average orientation of the base of the head, and eventually the body orientation, was caused to be biased about 28° to the opposite side. Because the shuttering was synchronized with the scanning motion, the scanning motion must be involved in the maintenance of orientation to light. The direction of the bias rules out a two-signal comparison mechanism of orientation and demonstrates that a deviation of the tip from the source direction must decrease, rather than increase, the illumination of the photoreceptors. These findings, and the ocellar morphology, require that the photoreceptors be located inside the hollow tube of pigmentation where they can be shadowed by the pigment during deviations of the tip. Focusing by the curved anterior end should cause a similar modulation of the illumination at this location. The occasional episodes of transverse phototaxis can be explained by the leakiness of the pigment walls to transverse illumination. Analysis of the motion of the anterior in the presence and absence of shuttering indicates that the orientation of the base of the head, due to the motion of the neck, is controlled by the signals generated during one or more cycles of the scanning motion of the head. The orientation may be regulated by the phase relationship between the photoreceptor signal and putative proprioceptive signals that indicate the bending in the head.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00188118
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  • 9
    Electronic Resource
    Electronic Resource
    Components of phototaxis of the nematode Mermis nigrescens (1990)
    Springer
    Journal of comparative physiology 167 (1990), S. 245-255 
    Details
    ISSN: 1432-1351
    Keywords: Undulatory locomotion ; Scanning motion ; Directed turn ; Orientation ; Phototaxis ; Klinotaxis ; Photomovement ; Nematode
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The gravid females of Mermis are positively phototaxic at the time of their migration to egglaying sites in vegetation on which their grasshopper hosts feed. On a horizontal felt surface, segments of the path traced by the tail are oriented approximately towards a source of monochromatic light in the 350–540 nm region, but are not oriented at longer wavelengths and in the dark. The components of this phototaxis include locomotion by the posterior 4/5 of the body, orientational bending of the neck region while the anterior is held above the substrate, and a scanning motion (bending) of the head region (anterior 2 mm). Like other nematodes and snakes, propulsion is associated with posteriorly propagated body waves, but unlike other animals known, the waves tend to lie perpendicular to a felt surface, and unlike other nematodes, contact with the surface is on the female's ventral surface. The body waves are initiated by the motion of the anterior 1/5 (15 mm) of the body, the average orientation of which determines the path of the following 4/5. During phototaxis, the anterior tip is swung both sideways and vertically about the direction towards the light source. The tip motion is a result of a scanning motion of the head and a slower orientational bending of the neck. The base of the head appears to be actively directed towards the source by the bending of the neck. This behavior can resolve two light sources positioned 120° apart but not 90° apart. The scanning motion of the head is independent of neck orientation and appears to enhance the probability of discovering the direction of a new source. Discovery is followed by a directed turn of the base of the head towards the source which is initiated by the bending of the neck. Locomotion of the body follows the path of the anterior through the turn and phototaxis is thus initiated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00188117
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  • 10
    Electronic Resource
    Electronic Resource
    Unique locomotory mechanism of Mermis nigrescens, a large nematode that crawls over soil and climbs through vegetation (1994)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 222 (1994), S. 133-148 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Females of Mermis nigrescens, a nematode parasitic on grasshoppers, climb through terrestrial vegetation where they lay their eggs. The 100-mm-long body of these nematodes bridges gaps in this three-dimensional substratum, and crawls efficiently over planar surfaces. The nematodes do not use the classical undulant pattern of nematode locomotion as one coordinated unit; instead they propel themselves in several independent, locally controlled zones that propagate posteriorly. A repeated motion of their anterior end laces the body around fixed objects at which force may be applied. Propulsive force is applied to objects as the body glides past the contact site. Intermediate loops are elevated above the surface where they cannot contribute to propulsion. These loops rise and fall with time due to varying differences in propulsive forces between the contact sites.Forces are applied to the objects by internally generated bending couples that are propagated along the trunk, propelling the body in a cam-follower mechanism. Bending couples are generated by the contraction of ventral or dorsal longitudinal muscle bands that apply compressive force to the cuticle. The muscle bands, consisting of a single layer of obliquely striated muscle cells, are closely applied to the cuticle and are separated from it only by a fibrous basal lamina and a thin extension of a hypodermal cell. The myofilaments of each sarcomere are parallel to the body axis and attached perpendicularly via dense bodies (z-line equivalents) to the basal lamina, which in turn is fixed to the cuticle via filaments passing through the hypodermal cytoplasm, Consequently, forces are transmitted laterally to the cuticle over the entire length of the muscle, compressing it parallel to the surface without need for attachment to the terminal ends of the muscle cells. Thus the muscles are engineered for local control of bending and avoidance of buckling. There is evidence that the motor nervous system of Mermis may not be as simple as in classical nematode examples, which may explain why Mermis is capable of a much more localized control of locomotory motion. © 1994 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1052220203
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