tokens: Ninety - six Swiss - Webster mice ( 30 - 35 g , 6 - 8 wk ) , were randomized into 6 groups 1 ) saline ( control ) , 2 ) NTG immediately after learning , 3 ) NTG 3 h after learning , 4 ) NTG and NIMO , 5 ) vehicle , and 6 ) NIMO alone .