On the ability of choline and its analogues to interact with muscarinic cholinergic receptors in the rat brain.

Choline displaced [3H]QNB binding from rat brain muscarinic receptors competitively, (Ki = 460 microM) but it was only 1/1000th as potent as ACh. Deanol was an extremely weak displacer of [3H]QNB binding while hemicholinium-3 was 50 times more potent than choline. Although brain levels of choline are well below its Ki value for muscarinic receptors, choline may directly interact with rat brain muscarinic receptors in some circumstances.