Fig 1.
Schematic drawings of the spontaneous place recognition (SPR) test and the delay-interposed radial arm maze (dRAM) task.
The delay length was 6 h in both tests. Roman numerals above each arrowhead show drug injection times. I: before the sample phase (or first-half performance); IIa: immediately after the sample phase (or first-half performance); IIb: 2 h after the sample phase (or first-half performance); III: before the test phase (or second-half performance). (A) In the SPR test, a white-black striped pattern was put on a sidewall of the arena as an absolute spatial cue. The test consisted of a sample phase (15 min), a delay period, and a test phase (5 min) and two identical objects were used throughout the test. In the test phase, one of the objects was moved to a novel position in the arena. (B) In the dRAM task, after the rat freely made four correct choices (gray arms), it was kept in a waiting cage. After the delay, it was required to visit the rest of arms (black arms) without reentering the arms visited already.
Fig 2.
Locations of the tips of injection cannulae.
Drugs were infused into the dorsal hippocampus in both experiments 1 and 2. (A) A photomicrograph showing a typical example of injection site. (B) Black dots denote tips of injection cannulae in each animal. Numbers in the left represent anteroposterior distance (mm) from bregma [12].
Fig 3.
Effects of ANI, DRB and EME on the discrimination performance in the spontaneous place recognition test with 6 h and 5 min-delays.
Effects of ANI (A, B), DRB (C, D), and EME (E, F) for the 6 h-delay (A, C, E) and the 5 min-delay (B, D, F). Data are shown as mean ± SEM. * p < .05, ** p < .01 vs. chance (50%).
Fig 4.
Effects of ANI on the second-half performance in the 6 h delay-interposed radial arm maze task.
(A-C) Effects of ANI on the second-half performance in the 6 h-delayed task. (D-F) Effects of ANI on the second-half performance in the state-dependency test. (G-H) Effects of ANI on performance in the non-delayed radial arm maze task. (A, D) Number of correct choices in the first four choices. (B, E) Number of across-half errors. (C, F) Number of within-half errors. (G) Number of correct choices in the first eight choices. (H) Number of errors. Data are shown as mean ± SEM. * p < .05, ** p < .01 vs. Ringer condition.
Fig 5.
Effects of DRB on the second-half performance in the 6 h delay-interposed radial arm maze task.
(A) Number of correct choices in the first four choices. (B) Number of across-half errors. (C) Number of within-half errors. Data are shown as mean ± SEM. * p < .05 vs. DMSO condition.
Fig 6.
Effect of EME on the second-half performance in the 6 h delay-interposed radial arm maze task.
(A-F) Effect of EME on the second-half performance in the 6 h-delayed task. (G-I) Effect of EME on the second-half performance in the state-dependency test. (J-K) Effect of EME on the performance in the non-delayed task. (A, D, G) Number of correct choices in the first four choices. (B, E, H) Number of across-half errors. (C, F, I) Number of within-half errors. (J) Number of correct choices in the first eight choices. (K) Number of errors. Data are shown as mean ± SEM. * p < .05, ** p < .01 vs. saline (SAL) condition.
Fig 7.
Summary of the results of the present study.
↓: impairment by the inhibitor. →: no impairment.–: not examined. PSI: protein synthesis inhibitor. mRNA-SI: mRNA synthesis inhibitor. Short-term memory (STM) in the SPR test was estimated through the effect of drugs on performance with a 5 min-delay. In the radial maze task, STM was estimated using the effect of drugs on performance in the non-delayed task or on the number of within-half errors in the 6 h-delayed task.