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  • 1
    Electronic Resource
    Electronic Resource
    Agmatine recognizes α2-adrenoceptor binding sites but neither activates nor inhibits α2-adrenoceptors (1994)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 351 (1994), S. 10-16 
    Details
    ISSN: 1432-1912
    Keywords: Key words Agmatine ; α2-Adrenoceptor binding sites ; α2-Adrenoceptors ; Clonidine-displacing substance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract It has been suggested that agmatine (decarboxylated arginine) is an endogenous clonidine-displacing substance (CDS) which recognizes α2-adrenoceptor and non-adrenoceptor, imidazoline binding sites. We have examined the effect of agmatine at α2-adrenoceptor binding sites and pre- and postjunctional α2-adrenoceptors. Agmatine produced a concentration-dependent inhibition of 1 nmol/l 3H-clonidine binding to both rat (pKi–5.10±0.05) and bovine (pKi–4.77±0.38) cerebral cortex membranes. However, agmatine (0.1–100 μM) failed to activate pre-junctional α2-adrenoceptors regulating transmitter release in the guinea-pig isolated ileum and rat isolated vas deferens, nor did it activate postjunctional α2-adrenoceptors of the porcine isolated palmar lateral vein which mediate contraction or inhibition of forskolin-stimulated cyclic AMP formation. High concentrations of agmatine (10–30-fold the pKi at α2-adrenoceptor binding sites) failed to influence α2-adrenoceptor activation by either clonidine or UK-14304 (5-bromo-6-[2-imidazolin-2-ylamino]-quinoxaline bitartrate) in any of the peripheral preparations examined. Moreover, even in a preparation where an interaction with α2-adrenoceptor binding sites on cell membranes can be demonstrated, the rat cerebral cortex, agmatine failed to inhibit forskolin-stimulated cyclic AMP in the intact tissue or affect the inhibition produced by the selective α2-adrenoceptor agonist UK-14304. Agmatine was also devoid of agonist activity in two preparations, the rat isolated thoracic aorta and the rat isolated gastric fundus, in which CDS has been reported to produce non-adrenoceptor effects. Thus, we have confirmed that agmatine recognizes α2-adrenoceptor binding sites and, therefore, is a CDS. However, since agmatine is devoid of pharmacological activity at either peripheral or central α2-adrenoceptors it can not account for earlier reports suggesting that brain-derived CDS can activate α2-adrenoceptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00169058
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Responsiveness of cells in the cat's superior colliculus to textured visual stimuli (1979)
    Springer
    Experimental brain research 37 (1979), S. 231-240 
    Details
    ISSN: 1432-1106
    Keywords: Cat superior colliculus ; Visual texture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Responses to texture motion (visual noise) were investigated in the superior colliculus of paralysed cats, lightly anaesthetized with N2O/O2 supplemented with pentobarbitone or Althesin. Within the superficial layers two classes of texture-sensitive neurones were found: Type I units with weak responses to noise, often related to specific elements in the texture and Type II units which were driven independently of the texture structure, and tended to be recorded deep to the Type I units. Type III units recorded from the deep collicular layers were insensitive to texture. Anatomical bases for this differential sensitivity and the notion of two collicular subsystems are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00237710
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Differential responsiveness of cells in the visual zones of the cat's LP-pulvinar complex to visual stimuli (1981)
    Springer
    Experimental brain research 43 (1981), S. 25-33 
    Details
    ISSN: 1432-1106
    Keywords: Cat ; LP-pulvinar complex ; MIN ; Visual texture ; Receptive field properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Multiple visual field representations are contained within the feline LP-pulvinar complex; regions differentiated by their afferent and efferent connectivity patterns as the striate-, tecto- and retino-recipient zones. Cell responses from these visuotopic zones were investigated in immobilized cats under N2O/O2 supplemented with pentobarbitone or Althesin, using spot, bar and textured stimuli. Response fields recorded within the LP-pulvinar complex were classified as diffuse, concentric, movement-, direction- or orientation-sensitive. Concentric receptive fields were further classified as sustained (X), transient (Y) or tonic/phasic W-cells. Direction-and movement-sensitive cells predominated in the striate- and tecto-recipient zones, respectively. Motion of noise fields, or noise bars against an identical stationary noise background elicited vigorous responses from cells in the striate zone, many showing a preference for noise stimuli. In contrast, cells from the tectal zone and other divisions of the LP-pulvinar complex were insensitive to noise. The retino-recipient zone at the lateral margin of the pulvinar nucleus was characterized by cells with concentric receptive fields, the majority exhibiting properties similar to W-cells in the LGNd. The evidence supports the notion of functional subdivision within the LP-pulvinar complex corresponding to the visuotopically organized regions defined by their connectivity patterns. Consideration of the retino-recipient zone as an extension of the LGNd-MIN complex is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238806
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Agmatine recognizes α2-adrenoceptor binding sites but neither activates nor inhibits α2-adrenoceptors (1995)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 351 (1995), S. 10-16 
    Details
    ISSN: 1432-1912
    Keywords: Agmatine ; α2-Adrenoceptor binding sites ; α2-Adrenoceptors ; Clonidine-displacing substance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract It has been suggested that agmatine (decarboxylated arginine) is an endogenous clonidine-displacing substance (CDS) which recognizes α2-adrenoceptor and non-adrenoceptor, imidazoline binding sites. We have examined the effect of agmatine at α2-adrenoceptor binding sites and pre- and postjunctional α2-adrenoceptors. Agmatine produced a concentration-dependent inhibition of 1 nmol/l 3H-clonidine binding to both rat (pKi–5.10+-0.05) and bovine (pKi–4.77+-0.38) cerebral cortex membranes. However, agmatine (0.1–100 μM) failed to activate pre-junctional α2-adrenoceptors regulating transmitter release in the guinea-pig isolated ileum and rat isolated vas deferens, nor did it activate post-junctional α2-adrenoceptors of the porcine isolated palmar lateral vein which mediate contraction or inhibition of forskolin-stimulated cyclic AMP formation. High concentrations of agmatine (10–30-fold the pKi at α2-adrenoceptor binding sites) failed to influence α2-adrenoceptor activation by either clonidine or UK-14304 (5-bromo-6-[2-imidazolin-2-ylamino]-quinoxaline bitartrate) in any of the peripheral preparations examined. Moreover, even in a preparation where an interaction with α2-adrenoceptor binding sites on cell membranes can be demonstrated, the rat cerebral cortex, agmatine failed to inhibit forskolin-stimulated cyclic AMP in the intact tissue or affect the inhibition produced by the selective α2-adrenoceptor agonist UK-14304. Agmatine was also devoid of agonist activity in two preparations, the rat isolated thoracic aorta and the rat isolated gastric fundus, in which CDS has been reported to produce non-adrenoceptor effects. Thus, we have confirmed that agmatine recognizes α2-adrenoceptor binding sites and, therefore, is a CDS. However, since agmatine is devoid of pharmacological activity at either peripheral or central α2-adrenoceptors it can not account for earlier reports suggesting that brain-derived CDS can activate α2-adrenoceptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00169058
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
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