Chronic fluoxetine treatment of aged mice maintains stimulus response potentiation. A, Experimental time line. SRP was tested at 6 months, with or without 3 months of fluoxetine treatment, or at 9 months untreated or after 3 or 6 months of fluoxetine treatment. B, Fluoxetine treatment (yellow squares) had no significant effect on SRP in 6-month-old mice measured on Day 5 (Day 5 = 1.95 ± 0.23-fold increase over Day 1; n = 6) compared with untreated 6-month-old mice (brown circles; Day 5 = 1.6 ± 0.19-fold increase over Day 1; unpaired two-tailed Student's t test p = 0.256, n = 10). C, Three months of fluoxetine treatment had no statistically significant effect on SRP in 9-month-old mice (green diamonds; Day 5 = 1.35 ± 0.11-fold increase over Day 1; n = 11) compared with untreated 9-month-old mice (black circles; Day 5 = 1.08 ± 0.32-fold increase over Day 1; t test p = 0.339, n = 5), but 6 months of treatment significantly increased SRP in 9-month-old (blue squares) mice compared with untreated mice (Day 5 = 1.95 ± 0.39-fold increase over Day 1; t test p = 0.0405, n = 5).