The present invention provides a method of specifically potentiating an N-type Ca.sup.2+ channel activity, which includes administering, to a subject, a compound of the following formula (I): wherein R.sup.1 is lower alkyl, aryl, ar(lower)alkoxy or a heterocyclic group, the above groups being optionally substituted by halogen, R.sup.2 is hydrogen atom or lower alkyl, R.sup.3 is cyclo(lower)alkyl, aryl or ar(lower)alkyl, the above groups being optionally substituted by halogen, A is --CO--, --SO.sub.2-- or lower alkylene, and Y shows --CO--, --SO.sub.2-- or --CONH-- (compound (I)), a salt thereof, a prodrug thereof or a solvate thereof; a method for the prophylaxis or treatment of brain disorders such as dementia and amnesia, which includes such administration; and a screening method particularly useful for screening a compound having a similar effect as compound (I).