NON-ACETYLCHOLINE DISPLACEABLE (3)[H]EPIBATIDINE BINDING IN THE RAT-BRAIN

Using autoradiography two types of [H-3]epibatidine binding in rat bra in was found, the by far most widespread was nicotine displaceable, an d represented nicotinic cholinergic receptors, probably the two subtyp es alpha(4) beta(2) and alpha(3) beta(4). Using acetylcholine and nico tine in concentrations able to displace (3)[H]epibatidine from the alp ha(4) beta(2) and alpha(3) beta(4) subunits, in a few brain structures a non-acetylcholine and non-nicotine displaceable (3)[H]epibatidine b inding was found. The binding was almost exclusively localised to the medial and lateral habenula, interpeduncular nucleus and pineal gland; at 0.1 nM (3)[H]epibatidine it represented about 40% of the total (3) [H]epibatidine binding. A literature search directed at neurotransmitt ers in habenula did not demonstrate any neurotransmitter with this ana tomical distribution in the brain, suggesting that the non-acetylcholi ne displaceable (3)[H]epibatidine binding represents a binding site, n ot previously described. (C) 1998 Elsevier Science Ireland Ltd.