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  • 3H-Clonidine binding sites  (1)
  • 5-HT1A, 5-HT1B, 5-HT1C, 5-HT2 receptor subtypes  (1)
  • 1
    Electronic Resource
    Electronic Resource
    5-HT1A-receptors mediate stimulation of adenylate cyclase in rat hippocampus (1986)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 333 (1986), S. 335-341 
    Details
    ISSN: 1432-1912
    Keywords: Postsynaptic 5-HT1 receptors ; Adenylate cyclase ; Rat hippocampus ; 5-HT1A, 5-HT1B, 5-HT1C, 5-HT2 receptor subtypes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Serotonin (5-HT) stimulated adenylate cyclase activity in homogenates of rat hippocampus. This effect was pharmacologically characterised with a series of agonists and antagonists of various structural classes. 2. These compounds where also tested in radioligand binding studies using selective ligands for the various subtypes of 5-HT1 and 5-HT2 receptors. 5-HT1A, 5-HT1B and 5-HT1C recognition sites were labelled with [3H]8-OH-DPAT ([3H]8-hydroxy-2-(di-n-propylamino)-tetralin) in pig cortex membranes, [125I]CYP([125I]iodocyanopindolol) in rat cortex and [3H]mesulergine in pig choroid plexus membranes, respectively. 3. The rank order of potency of 13 agonists stimulating adenylate cyclase activity in homogenates of rat hippocampus was in good agreement with the rank order of affinity of these agonists for the 5-HT1A binding site: N,N-dipropyl-5-carboxamidotryptamine (DP-5-CT)〉5-carboxamidotryptamine (5-CT)〉8-OH-DPAT〉5-HT〉 5-methoxytryptamine (5-OCH3T)〉d-LSD〉5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole (RU 24969)〉α-methylserotonin (α-CH3-5-HT)〉dopamine〉2-methylserotonin (2-CH3-5-HT). The correlation between the respective potencies and affinities of these agonists was r=0.934, P〈0.001. 4. There was no correlation between stimulation of adenylate cyclase activity by these agonists and their affinity for 5-HT1B, 5-HT1C or 5-HT2 binding sites. r=0.381–0.108, P〈0.20–0.73. 5. Potent antagonists at D-1 receptors (SCH 23390), 5-HTM receptors (ICS 205-930), 5-HT2-receptors (ketanserin) and 5-HT1C-receptors (mesulergine) antagonised the 5-HT stimulated adenylate cyclase activity only at very high concentrations. In contrast, spiperone and metitepin were potent antagonists of the effect of 5-CT and 5-HT on adenylate cyclase. The use of these selective antagonists allowed to exclude the possibility that 5-HT stimulates adenylate cyclase activity in rat hippocampus through D-1, 5-HTM, 5-HT2 or 5-HT1C receptors. 6. These data support the concept that 5-HT stimulated adenylate cyclase activity in rat hippocampus is mediated by a 5-HT1A receptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00500006
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Lesioning of serotoninergic and noradrenergic nerve fibres of the rat brain does not decrease binding of 3H-clonidine and 3H-rauwolscine to cortical membranes (1985)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 328 (1985), S. 229-235 
    Details
    ISSN: 1432-1912
    Keywords: α2-Adrenoceptors ; 3H-Clonidine binding sites ; 3H-Rauwolscine binding sites ; Noradrenergic neurons ; Serotoninergic neurons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary α2-adrenoceptors located presynaptically on nerve terminals are known to modulate the release of neurotransmitters from noradrenergic and serotoninergic neurons. The pre- and/or postsynaptic localization of binding sites for α2-adrenergic radioligands, the agonist 3H-clonidine and the antagonist 3H-rauwolscine, was investigated in the rat cerebral cortex by the use of specific neurotoxins. Intracerebroventricular ijections of 6-hydroxydopamine (6-OH-DA) and 5,7-dihydroxytryptamine (5,7-DHT) were used to destroy the noradrenergic and serotoninergic neurons, respectively, and the success of the treatment was controlled by measurement of tritium accumulation in cortex slices incubated with 3H-noradrenaline or 3H-serotonin. In cortical membranes, 3H-rauwolscine bound to a single site (K D about 5 nmol/l; B max 217–247 fmoles/mg protein), whereas 3H-clonidine bound to a high affinity site (K D 0.6–1.4 nmol/l) and a low affinity site (K D 6–10 nmol/l). The total number of high plus low affinity 3H-clonidine binding sites was about two thirds of the number of 3H-rauwolscine binding sites. 6-OH-DA treatment significantly increased the number of high affintiy 3H-clonidine binding sites without reducing the number of high plus low affinity binding sites, indicating a denervation supersensitivity. K D- as well as B max-values for 3H-rauwolscine remained unaltered after 6-OH-DA-treatment. Since an increase in postsynaptic α2-adrenoceptors due to 6-OH-DA-administration might have masked a loss of presynaptic α2-adrenergic binding sites, rats were chronically treated with high doses of clonidine in order to prevent a possible supersensitivity of postsynaptic receptors. Even under these conditions 6-OH-DA did not reduce the number of 3H-clonidine and 3H-rauwolscine binding sites. Injection of 5,7-DHT had no influence on binding parameters of 3H-clonidine and 3H-rauwolscine. It is concluded that in the cerebral cortex the number of postsynaptic α2-adrenoceptors is much greater than that of presynaptic α2-adrenoceptors. Therefore, the changes in the number of presynaptic α2-adrenoceptors due to destruction of noradrenergic or/and serotoninergic neurons cannot be detected by equilibrium binding studies with 3H-clonidine or 3H-rauwolscine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00515546
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    Paper (German National Licenses)
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