Fluoxetine enhances memory processing in mice

Fluoxetine (FLU) increases brain concentrations of serotonin by blocking its uptake, without appreciably affecting the dopamine or norepinephrine systems. The present experiments provide evidence that a subcutaneous injection of FLU enhanced post-memory processing ("consolidation") and retrieval, but not acquisition in young adult mice. FLU (15 mg/kg) enhanced 1-week memory retention when injected 2 min post-training. Similar enhancement was obtained with intracerebroventricular injection (20 micrograms per mouse). FLU enhanced retention when administered prior to training (1-5 mg/kg). FLU (2.5 mg/kg) enhanced recall scores when injected 1 h before the 1-week retention test, indicating an enhancing effect on memory retrieval. Neither the pre-training nor pre-testing effects depended on improved acquisition, since FLU did not improve acquisition of T-maze foot-shock avoidance over the dose range 0.5-35 mg/kg. The sensitive period for post-training enhancement by FLU (15 mg/kg) was less than 90 min, as shown by the temporal gradient typical of memory-enhancing drugs. The amnesia induced by a protein synthesis inhibitor anisomycin, or by an anticholinergic drug scopolamine, was blocked by FLU (15 mg/kg) injected post-training. Finally, FLU (15 mg/kg) injected after one-trial passive avoidance training enhanced 1-week retention, demonstrating effectiveness in this task as well as in the active avoidance task.