tokens: One week later , they received repeatedly vehicles ( saline , DMSO , saline + DMSO ) , scopolamine ( 2 microg / 0 . 5 microl saline / side ; 30 min before training ) , ritanserin ( 2 , 4 and 8 microg / 0 . 5 microl DMSO / side ; 20 min before training ) and scopolamine ( 2 microg / 0 . 5 microl ; 30 min before ritanserin injection ) + ritanserin ( 4 microg / 0 . 5 microl DMSO ) through cannulae each day .