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  • Electronic Resource  (4)
  • 1990-1994  (4)
  • 1925-1929
  • Cell & Developmental Biology  (2)
  • Adsorption ofproteins  (1)
  • Antagonism  (1)
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  • Electronic Resource  (4)
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  • 1
    ISSN: 1432-2072
    Keywords: Nicotine ; Cholinergic receptors ; nAChRs ; Drug discrimination ; Acute tolerance ; Rats ; Antagonism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Current concepts concerning nicotine's CNS mechanism(s) of action suggest that this drug produces its effects via an interaction at nicotinic-cholinergic receptors (nAChRs) sensitive to acetylcholine. In vitro research further suggests that, following its initial agonist effect, this cholinergic drug may also induce a rapid desensitization of the nAChR similar to that of acetylcholine, resulting in termination of its pharmacological effect. Research described in this paper provides evidence of this secondary desensitization process in vivo by demonstrating nicotine's ability to induce acute tolerance in a Discriminative Stimulus (DS) paradigm. The ability of nicotine (400 µg/kg, SC) to elicit DS control of behavior in a two-lever operant procedure was significantly reduced via a challenge dose (800 µg/kg, SC) of nicotine administered 15–180 min before the training dose. Twenty-three of 52 rats demonstrated this phenomenon. The time to develop acute tolerance varied, providing additional evidence that these effects may be contingent upon individual rat variability. In addition, physostigmine was also observed to induce a similar desensitization in a random population of desensitizing rats. Lastly, there were no differences between desensitizers and non-desensitizers in relation to the ability of mecamylamine (1000 µg/kg, SC) to antagonize the DS, while in both populations of rats scopolamine (100 µg/kg, SC) failed to antagonize the DS.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 270 (1992), S. 353-363 
    ISSN: 1435-1536
    Keywords: Adsorption ofproteins ; albumin ; chromiumhydroxide ; γ-globulin ; hematite ; lysozyme
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The adsorption of ovalbumin, γ-globulin, and lysozyme on uniform spherical hematite and chromium hydroxide particles in aqueous media has been studied as a function of the pH at a constant ionic strength. The uptake of ovalbumin and γ-globulin was greatest at their isoelectric points and differed little at 10−2 and 10−3 mol dm−3 NaNO3. The adsorption of lysozyme was strongly influenced by the ionic strength. The deposition of ovalbumin on hematite in the presence of Mg (NO3)2 was significantly greater than that with NaNO3 under otherwise comparable conditions. Dialysis experiments with ovalbumin against magnesium nitrate solutions showed Mg2+ to be specifically bound to the protein. The shapes of isotherms indicated monolayer coverage for ovalbumin and multilayer coating for lysozyme for both adsorbents. The shapes of isotherms of γ-globulin on hematite point to a rearrangement of the protein on the particle surface, while a monolayer was found on chromium hydroxide particles.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 203 (1990), S. 211-217 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A unique pathway that utilizes endoplasmic reticulum (ER) networks is proposed for screening pigment granule formation in the retina of adult Eumesosoma roeweri. Smooth endoplasmic reticulum (SER) functions to transport pigment particles to the formative site. Each site is composed of concentric, interconnected rings of SER that are filled with dense-cored, spherical pigment particles. Formation of the screening pigment granule begins by the release of particles from the innermost rings of carrier SER. Continued release followed by fusion and condensation of the pigment particles results in the formation of a mature pigment granule.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0003-276X
    Keywords: Spermatozoa ; Epididymis ; Grey short-tailed opossum ; Marsupial ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In order to understand the evolutionary significance of sperm-pairing in American marsupials, an ultrastructural investigation was made of this process in the South American grey short-tailed opossum, Monodelphis domestica. One epididymis from each animal (5) was fixed for light and electron microscopy and divided into 18 segments. The contralateral tract was divided into similar segments and assessments made of the total number of spermatozoa and the proportion of sperm-pairs. The mean total sperm number was 4.20 ± 0.62 × 106/epididymis. Sperm-pairing commenced around segment 9 in the proximal corpus epididymidis and reached a maximum of 80% in the caudal sperm storage region of the duct. The sperm-pairing process was characterised by four stages. Spermatozoa exhibited parallel alignment as indicated by the positioning of identical cross-sections of sperm heads. This was followed by close apposition with acrosomal faces parallel rather than opposite. Rotation of the sperm heads around each other then apparently occurred as indicated by the morphological alignment of sections of paired sperm heads. Sperm-pairing was complete when the acrosomal faces were precisely aligned and joined. Misalignment and failure to pair was observed in about 20% of spermatozoa in the cauda epididymis. Such a complex sperm-pairing process may ensure that conjugated spermatozoa are precisely aligned so that flagella movement can be accurately coordinated for maximal progressive motility. © 1993 Wiley-Liss, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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