Autoradiographic localization of the GABA A receptor agonist [ 3H]muscimol in rat cerebral vessels

Abstract

By the use of combined in vitro radioreceptor binding and autoradiographic techniques with [ 3H]muscimol as a ligand, we analyzed the distribution of GABA A receptor sites in the arteries of the circle of Willis as well as in the arteries and arterioles of the pial-arachnoid membrane in the rat. [ 3H]Muscimol was bound by sections of rat cerebral vessels in a manner consistent with the existence of GABA A receptors, with K d and B max values of 46 nM and 0.60 pmol/mg tissue respectively. [ 3H]Muscimol was bound by the medial layer of cerebral arteries, while no specific binding was observed in the intima, the adventitia and the adventitial-medial border. These findings suggest that the vasodilatory action of GABA on in vitro preparations of cerebral vessels is mediated by muscular receptor sites. The posterior cerebral arteries are richer in [ 3H]muscimol binding sites than the anterior ones. Pial-arachnoid arterioles, which are of critical importance in controlling local cerebral blood flow, did not exhibit any significant binding of [ 3H]muscimol. These results may explain the difficulty in manipulating pharmacologically the cerebral tissue perfusion in intact animals using GABAergic agonists.