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  • 1
    Electronic Resource
    Electronic Resource
    The selective dopamine D2 receptor antagonist raclopride discriminates between dopamine-mediated motor functions (1986)
    Springer
    Psychopharmacology 90 (1986), S. 287-294 
    Details
    ISSN: 1432-2072
    Keywords: Raclopride ; Substituted benzamides ; Dopamine D2 receptors ; Catalepsy ; Apomorphine ; 3H-spiperone ; 3H-NPA ; Dopamine turnover
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The actions on central dopamine (DA) mechanisms of raclopride, a new substituted benzamide, were studied by means of behavioural and biochemical methods in the rat. Raclopride blocked the in vitro binding of the dopamine D2 antagonist 3H-spiperone (IC50=32 nM), but not of the unselective D1 antagonist 3H-flupenthixol (IC50〉100,000 nM) in rat striatum, and failed to inhibit striatal DA-sensitive adenylate cyclase in vitro (IC50〉100,000 nM). Raclopride caused a dose-dependent increase in the DA metabolites HVA and DOPAC in the striatum and olfactory tubercle. Behavioural studies showed that raclopride discriminates between the motor behaviours induced by the DA agonist apomorphine. Thus, unlike haloperidol, raclopride blocked apomorphine-induced hyperactivity at considerably lower doses than those inhibiting oral stereotypies. Moreover, raclopride showed a high separation between the doses for blockade of apomorphine-induced hyperactivity and those inducing catalepsy in rats. Raclopride caused a dose-dependent blockade of the specific binding of 3H-spiperone and 3H-N-n-propylnorapomorphine (3H-NPA) in vivo at doses similar to those blocking the behavioural effects of apomorphine. The maximal blockade of 3H-spiperone binding in vivo was lower for raclopride than for haloperidol. Raclopride caused a greater inhibition of 3H-NPA than of 3H-spiperone in vivo binding in the striatum. It is suggested that the ability of raclopride to discriminate between different DA-mediated functions may be attributed to a preferential blockade of a subclass of functionally coupled dopamine D2 receptors in striatal as well as in extrastriatal brain regions in the rat.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00179179
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  • 2
    Electronic Resource
    Electronic Resource
    Is inhibitio of striatal synaptosomal tyrosine hydroxylation by dopamine agonists a measure of dopamine autoreceptor function? (1985)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 331 (1985), S. 12-19 
    Details
    ISSN: 1432-1912
    Keywords: Presynaptic dopamine autoreceptors ; Tyrosine hydroxylase ; Rat striatum ; Dopamine agonists ; Dopamine antagonists
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Sumamry Rat striatal synaptosomal tyrosine hydroxylation was inhibited dose- and pH dependently by a number of dopamine agonists. The catecholic agonists apomorphine and (−)N-n-propylnorapomorphine inhibited synaptosomal tyrosine hydroxylase completely, with IC50 values of around 0.3 μmol/l at pH 6.6. The noncatechol agonists pergolide and bromocriptine and the putative dopamine autoreceptor agonists 3-PPP(−), 3-PPP(+), HW-165 and B-HT 920 produced only partial inhibition of synaptosomal tyrosine hydroxylation at high concentrations. Comparison of the inhibition of synaptosomal and soluble tyrosine hydroxylase indicated that the inhibition produced by apomorphine could be ascribed to a direct effect on the enzyme, whereas this was not the case for the noncatechol agonists. The inhibition produced by pergolide and 3-PPP(−) was not antagonised by either dopamine receptor or alpha-adrenoceptor antagonists. The present results have been compared with results reported in the literature for inhibition of synaptosomal tyrosine hydroxylation and for two other tests of dopamine autoreceptor agonist activity (inhibition of dopamine release from striatal slices in vitro, and inhibition of the gamma-butyrolactone induced increase in dopamine synthesis in vivo). It is concluded that inhibition of striatal synaptosomal tyrosine hydroxylation by dopamine agonists does not fulfil the criteria required for it to be considered as a useful measure of dopamine autoreceptor function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00498846
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  • 3
    Electronic Resource
    Electronic Resource
    Comparison of the effects of haloperidol, remoxipride and raclopride on “pre”- and postsynaptic dopamine receptors in the rat brain (1988)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 337 (1988), S. 379-384 
    Details
    ISSN: 1432-1912
    Keywords: Dopamine receptors ; Gamma-butyrolactone ; Haloperidol ; Raclopride ; Remoxipride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The ability of the dopamine receptor antagonists haloperidol, raclopride and remoxipride to prevent the B-HT 920-induced decrease in striatal and limbic L-DOPA accumulation in gamma-butyrolactone (GBL)- and NSD 1015-treated rats (termed ‘GBL-reversal’) was used to define the effects of these compounds on “presynaptic” dopamine receptors. The doses of the dopamine antagonists producing antagonism of GBL-reversal were in each case roughly similar to the doses required to increase dopamine turnover in striatal and limbic areas. The potencies of haloperidol, raclopride and remoxipride in the GBL model were compared with their potencies in behavioural models for postsynaptic dopamine receptors. Haloperidol produced antagonism of GBL-reversal over a similar dose range to that required for antagonism of apomorphine-induced hyperactivity and stereotypy syndromes. Raclopride was effective in the order of potency: antagonism of apomorphine-induced hyperactivity 〉 antagonism of GBL-reversal 〉 antagonism of apomorphine-induced stereotypy. For remoxipride, the dose-response curve for antagonism of GBL-reversal was superimposable over that for antagonism of apomorphine-induced stereotypies, with an ED50 value about 12 times higher than that for antagonism of apomorphine-induced hyperactivity. Thus, the relative potencies of dopamine receptor antagonists at “pre-” and postsynaptic dopamine receptors vary considerably from compound to compound.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00169527
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