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P2-Receptor-mediated inhibition of noradrenaline release in the rat hippocampus

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Abstract

Experiments on hippocampal slices were carried out in order to find out whether the release of noradrenaline in the hippocampus can be modulated through P2-receptors. The slices were preincubated with [3H]-nor-adrenaline, superfused with medium containing desipramine (1 µM), and stimulated electrically, in most experiments by 4 pulses/100 Hz. The adenosine A1-receptor agonist N6-cyclopentyl-adenosine (CPA) and the nucleotides ATP, adenosine-5’-O-(3-thiotriphosphate) (ATPγS) and adenosine-5’-O-(2-thiodiphosphate) (ADPβS) decreased the evoked overflow of tritium by up to 55 %. The adenosine A2a-agonist 2-p-(2-carboxyethyl)-phenethylamino-5’-N-ethylcarboxamido-adenosine (CGS 21680; 0.003-0.3 µM) caused no change. The concentration-response curve of CPA was shifted to the right by the A1-antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 3 nM) but not by the P2-receptor antagonists cibacron blue 3GA (30 µM) and reactive blue 2 (30 µM); the apparent pKB value of DPCPX against CPA was 9.0. In contrast, the concentration-response curve of ATP was shifted to the right by DPCPX (3 nM), apparent pKB 8.7, as well as by ciba-cron blue 3GA (30 µM), apparent pKB 5.2, and reactive blue 2 (30 µM), apparent pKB 5.6; the antagonist effects of DPCPX and cibacron blue 3GA were additive in a manner compatible with the blockade of two separate receptors for ATP. The same pattern was obtained with ATPγS: its concentration-response curve was shifted to the right by DPCPX as well as by cibacron blue 3GA and reactive blue 2. Suramin (300 µM) antagonized neither the effect of ATP nor that of ATPγS. The 5’-nucleotidase inhibitor α,β-methylene-ADP (100 µM) did not change the effect of ATP. Only cibacron blue 3GA (30 µM) but not reactive blue 2 (30 µM), given alone, consistently caused a small increase of the evoked overflow of tritium. Hippocampal slices degraded exogenous ATP, and this degradation was reduced by cibacron blue 3GA (30 µM), reactive blue 2 (30 µM) and suramin (300 µM). The results indicate that the noradrenergic terminal axons of the rat hippocampus possess P2-receptors in addition to the known A1-adenosine receptors. The presynaptic P2-receptors mediate an inhibition of noradrenaline release, are activated by nucleotides but not nucleosides, and are blocked by cibacron blue 3GA and reactive blue 2. ATP and ATPγS act at both the A1- and the P2-receptors. An autoreceptor function of cerebral presynaptic P2-receptors remains doubtful.

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Received: 20 November 1996 / Accepted: 10 February 1997

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Koch, H., von Kügelgen, I. & Starke, K. P2-Receptor-mediated inhibition of noradrenaline release in the rat hippocampus. Naunyn-Schmiedeberg's Arch Pharmacol 355, 707–715 (1997). https://doi.org/10.1007/PL00005003

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  • DOI: https://doi.org/10.1007/PL00005003

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