Geissospermum vellosii stembark: anticholinesterase activity and improvement of scopolamine-induced memory deficits.

This study evaluated the cholinesterase inhibitory activity of an alkaloid-rich fraction of stembark from Geissospermum vellosii (PP), and its effect on memory tests in mice. PP inhibited rat brain and electric eel acetylcholinesterase, as well as horse serum butyrylcholinesterase in a concentration-dependent manner with mean IC(50) values of 39.3 microg/mL, 2.9 microg/mL, and 1.6 microg/mL, respectively. The main alkaloid with anticholinesterase activity in PP was isolated and identified as geissospermine. PP significantly reduced scopolamine-induced amnesia in the passive avoidance and Morris water maze tests, at 30 mg/kg i.p. (given 45 min before the test sessions). At the highest effective dose (60 mg/kg), administration of PP did not result in noticeable peripheral or central cholinergic side effects. Only after administration of 200 mg/kg, mice showed convulsions affecting the whole body followed by death. These results show that compounds present in G. vellosii stembark have anticholinesterase activity, and that they can revert cognitive deficits in a model of cholinergic hypofunction.