Effect of baclofen on in vitro noradrenaline release from rat hippocampus and cerebellum: an action at an ?(2)-adrenoceptor.
The release of [(3)H]noradrenaline from rat hippocampal synaptosomes by 25 mM K(+) and 5 ?M veratridine, but not by the Ca(2+) 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 ?(2)-adrenoceptor antagonists yohimbine and Wy25309 antagonised the action of clonidine and baclofen but not that of GABA. Specific binding of [(3)H]clonidine was displaced by Wy25309 and baclofen, but not by GABA. Specific binding of [(3)H]GABA in the presence of Ca(2+) was displaced by baclofen but not by Wy25309. It is concluded that baclofen is not a specific agonist at GABA(B) receptors in the brain.
Fung
S C
SC
University Laboratory of Physiology, Parks Rd, Oxford OX1 3PT, U.K.
Swarbrick
M J
MJ
Fillenz
M
M