Effect of baclofen on in vitro noradrenaline release from rat hippocampus and cerebellum: an action at an α2-adrenoceptor |
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Authors: | S-C Fung MJ Swarbrick M Fillenz |
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Institution: | University Laboratory of Physiology, Parks Rd, Oxford OX1 3PT, U.K. |
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Abstract: | The release of 3H]noradrenaline from rat hippocampal synaptosomes by 25 mM K+ and 5 μM veratridine, but not by the Ca2+ ionophore A23187 was depressed by baclofen. This depression was reversed by 8-Bromo-cAMP. This action of baclofen was stereospecific and mimicked both that of GABA in the presence of bicuculline and that of clonidine. The α2-adrenoceptor antagonists yohimbine and Wy25309 antagonised the action of clonidine and baclofen but not that of GABA. Specific binding of 3H]clonidine was displaced by Wy25309 and baclofen, but not by GABA. Specific binding of 3H]GABA in the presence of Ca2+ was displaced by baclofen but not by Wy25309. It is concluded that baclofen is not a specific agonist at GABAB receptors in the brain. |
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Keywords: | NA noradrenaline GABA 5-HT 5-hydroxytryptamine DMSO dimethyl sulfoxide HEPES cAMP adenosine 3′ 5′-monophosphate extracellular calcium ion concentration equilibrium dissociation constant of an inhibitor |
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