Unexpected potentializing effect of a tacrine derivative (9-amino-7-methoxy-1,2,3,4 tetrahydroacridine) upon the non-epileptic myoclonus in baboons Papio papio.

1. The influence of 7-methoxytacrine (7-MEOTA) on the non epileptic myoclonus of the Papio papio baboon was studied in 5 animals. 2. This type of myoclonus is thought to depend on a cholinergic system dysfunction since it can be induced by atropine and blocked by physostigmine. 3. 7-MEOTA, a tacrine derivative, is believed to display a conspicuous anticholinesterase activity but, surprisingly, it here potentiated the non epileptic myoclonus occuring either spontaneously or induced by atropine. 4. In baboons not spontaneously presenting the non epileptic myoclonus, 7-MEOTA induced the myoclonus in a fashion similar to atropine; such a myoclonus was blocked by physostigmine. 5. These data indicate a possible antagonist action of tacrine on the muscarinic acetylcholine receptor. From these data, it is suggested that caution is necessary when introducing a tacrine derivative in clinical practice.