CNS acetylcholine receptor activity in European medicinal plants traditionally used to improve failing memory

Certain Lamiaceous and Asteraceous plants have long histories of use as res toratives of lost or declining cognitive functions in western European syst ems of traditional medicine. Investigations were carried out to evaluate hu man CNS cholinergic receptor binding activity in extracts of those European medicinal plants reputed to enhance or restore mental functions including memory. Ethanolic extracts were prepared from accessions of these plants an d a number of other species related by genus. Amongst the plant extracts sc reened for contents able to displace [H-3]-(N)-nicotine and [H-3]-(N)-scopo lamine from nicotinic receptors and muscarinic receptors, respectively in h omogenates of human cerebral cortical cell membranes, the most potent extra cts, prepared from one accession of Melissa officinalis, three Salvia speci es and Artemisia absinthium had IC50 concentrations of <1 mg/ml. The displa cement curves of some extracts were comparable with that of carbamylcholine chloride, a potent acetylcholine analogue. Choline, a weak nicotinic ligan d (IC50 = 3 x 10(-4) M) was found in extracts of all plants studied at conc entrations of 10(-6)-10(-5) M. These concentrations could not account for n ot more than 5% of the displacement activity observed. Some extracts displa yed differential displacement at nicotinic and muscarinic acetylcholine rec eptors, with M. officinalis 0033 having the highest [H-3]-(N)-nicotine disp lacement value and Salvia elegans with the highest [H-3]-(N)-scopolamine di splacement value. There was also considerable variation in cholinoreceptor interactions between different accessions of a single plant species. Althou gh most plant extracts screened showed some nicotinic and muscarinic activi ty, only some showed dose-dependent receptor activity typical of materials with genuine cholinergic activity. (C) 2000 Elsevier Science Ireland Ltd. A ll rights reserved.