Comparison of the effects of cholinesterase inhibitors on [3H]MK-801 binding in rat cerebral cortex.

Huperzine A, a selective inhibitor of acetylcholinesterase, was recently demonstrated to exert an antagonist effect on N-methyl-D-aspartate (NMDA) receptor in rat cerebral cortex. In the present study, the effects of six cholinesterase inhibitors, e.g. huperzine A, huperzine B, tacrine, donepezil (E2020), physostigmine and galanthamine on [3H]dizocilpine (MK-801) binding to synaptic membrane of rat cerebral cortex were compared. Their IC50 values (mean +/- SD) were 36.9 +/- 12.1, 316.8 +/- 93.2, 33.2 +/- 3.7, 135.0 +/- 15.1, 50.4 +/- 7.4, and 3344 +/- 295 microM, respectively. The rank order of potency is tacrine approximately huperzine A > physostigmine > donepezil > huperzine B >> galanthamine. There is no correlation between their activities to inhibit [3H]MK-801 binding and to inhibit acetylcholinesterase (r = +0.563, P = 0.245). The results suggest that most cholinesterase inhibitors available exhibit an antagonist effect on NMDA receptor in rat cerebral cortex in addition to their inhibitory effect on acetylcholinesterase.