Post-training intrahippocampal injection of the class I and class II HDAC inhibitor TSA enhances long-term object-location memory. (A) Illustration of cannula placement in the dorsal hippocampus. Mice were allowed to recover for 1 wk after cannula implantation. Coronal brain slices were stained with cresyl violet. (B) Schematic diagram illustrating the object-location memory task during training (left) and testing (right). A visual cue was attached to one wall (“cue”). After the third training session, mice were injected with 0.5 µL of TSA (16.5 mM) or vehicle (50% Ethanol) per hippocampus. Testing was performed 24 h after training. (C) During the three training sessions, exploration time gradually decreased (P < 0.001) for both the object to be displaced (DO) and the nondisplaced object (NDO). No difference was observed between exploration time for the DO and NDO (P = 0.223). (D) Mice injected with TSA showed increase preference for the DO during the testing session relative to the last training session (P = 0.017), whereas vehicle-injected mice did not (P = 0.886). Equivalent exploration of both objects is indicated with a dashed line at 50% (“chance”). Error bars represent SEM.

Post-training intrahippocampal injection of the class I-selective HDAC inhibitor MS275 enhances long-term object-location memory. (A) During the three training sessions, exploration of the displaced object (DO) and the nondisplaced object (NDO) decreased (P < 0.001). No difference was observed in exploration time between the DO and the NDO (P = 0.647). (B) Preference for the DO increased in mice injected with MS275 (1 mM in 1% DMSO) during the testing session relative to the last training session (P = 0.019), whereas no increase in preference was observed in vehicle-injected mice (P = 0.539). Equivalent exploration of both objects is indicated with a dashed line at 50% (“chance”). Error bars represent SEM.