Non-ginsenoside nicotinic activity in ginseng species

Amongst the many different therapeutic applications of ginseng are benefici al effects on age-related cognitive impairments. Ageing in the brain is ass ociated with a loss of nicotinic receptor binding and receptor stimulation increases binding. Stimulation of the CNS (central nervous system) nicotini c receptor is considered to be beneficial in relation to symptomatic treatm ent and neuroprotection in age-associated cognitive disorders which involve a further receptor loss. We assessed Panax ginseng, Panax quinquefolium an d several chemical constituents of these plants for nicotinic activity base d on displacement of H-3-(-)nicotine from human brain cerebral cortex membr anes in vitro. Dose-dependent displacement was evident in crude ethanol ext racts of Panax ginseng and Panax quinquefolium. Assay of an extract of Pana x ginseng showed the plant to have affinity for both the nicotinic receptor , and to a lesser extent the muscarinic receptor (IC50 2.12 mg/mL and 5.25 mg/mL respectively), Activity was largely conserved after the extraction of choline and other water soluble quaternary ammonium compounds (QAC), indic ating that the activity of the plant extracts was not due to choline. Displ acement binding assay of some purified chemical constituents, including a n umber of ginsenosides, showed that these were not primarily responsible for Panax activity, The active chemical constituent has yet to be identified, but the demonstrated nicotinic activity of ginseng warrants further investi gation with reference to therapeutic activity in age-related conditions suc h as dementia. (C) 1999 John Wiley & Sons, Ltd.