In previous studies, 18-month-old rats have shown no significant retention 24 hours after the single acquisition trial in a one-trial discriminative reward learning task. In the present study, ten 18-month-old rats pretreated with 0.5 mg/kg MSF IP showed significantly better retention in terms of speed and errors than eleven 18-month-old rats pretreated with injection vehicle alone. However, twelve two-three-month-old rats pretreated with the same dose of MSF failed to show better retention than eleven two-three-month-old rats pretreated with vehicle alone.