Effect of MDL 73,745 on acetylcholine and biogenic amine levels in rat cortex

We postulate that the effect of cholinesterase inhibitors to ameliorate the cholinergic deficit in Alzheimer's disease is related to their ability to maintain long-lasting, non-toxic steady-state levels of acetylcholine in cortex. We investigated the effect of the cholinesterase inhibitor, MDL 73,745 (2,2,2-trifluoro-1-(3-trimethylsilylphenyl)ethanone), on the extracellular levels of acetylcholine, norepinephrine, dopamine and 5-hydroxytryptamine in the cerebral cortex of the rat by high-performance liquid chromatography coupled with electrochemical detection. The drug significantly increased acetylcholine levels above the baseline at 2 and 10 mg/kg s.c., but not at the 1 mg/kg dose. At both 2 and 10 mg/kg there was a good correlation between cholinesterase inhibition and acetylcholine increase in cortex. At the 2 and 10 mg/kg doses, the maximal cholinesterase inhibition was 64% and 77%, respectively, and the increase in acetylcholine release was 481% and 1016%, respectively. Norepinephrine and dopamine, but not 5-hydroxytryptamine levels, were also significantly increased by the 10 mg/kg dose. The increases of norepinephrine and dopamine levels reached a maximum of 124% and 370%, respectively, and continued for a period of at least 8 h. Cholinergic side-effects were most marked at the 10 mg/kg dose but were also noticeable at the 2 mg/kg dose in the form of fasciculations, tremor and splay.