Single bout of moderate‐intensity exercise facilitates memory consolidation via new protein synthesis in dorsal hippocampal CA1
Authors: Inoue Koshiro , Yamaguchi Akihiko , Morita Isao 
Published: November 2023

Background

An acute bout of exercise after learning boosts memory consolidation and thus improves long‐term memory. Some studies have shown that memory consolidation requires neuronal activity‐dependent protein synthesis in dorsal hippocampal CA1 region, and that an acute moderate‐intensity exercise (AME) enhances the regional neuronal activity. These findings provide a hypothesis that AME could boost memory consolidation via protein synthesis in the region. However, the hypothesis has not been proven because any helpful rodent models do not exist.

Purposes

This study, therefore, attempted to establish a rat model enhancing memory consolidation by AME (Exp.1), and tested the hypothesis by examining the effects of intrahippocampal CA1 administration of anisomycin (ANI), a protein synthesis inhibitor, on the AME‐induced memory consolidation (Exp.2).

Methods

All experiments used male Sprague‐Dawley rats (10‐week‐old). The rats were subjected to object location test (OLT) for the assessment of the memory consolidation, relying on rats' innate preference to explore the novel‐location object (N) compared with the familiar‐location object (F). The OLT was composed of one set of training and test session. In the training session, rats explored two identical objects for 5 min. In the test session conducted 24‐h later, only one object moved to a different position, and rats re‐explored these objects for 5 min. The time spent exploring the objects was measured in each session, and a discrimination ratio (DR) was calculated by dividing the amount of exploring time for N by the total amount of exploring time for both objects (N+F) in the test session. Exp.1: The rats performed 20 min of AME (20 m/min in treadmill) or of sedentary (Sed) immediately after the training session (n=12 for each condition). After 24‐h delay, their DRs were determined by the test session. Exp.2: Other rats were allocated to four conditions: 1) AME+ANI, 2) AME+placebo (Pla), 3) Sed+ANI, and 4) Sed+Pla (n=11–12 for each condition). ANI (25 μg/μl for 1μl) or Pla (saline) was administrated into bilateral dorsal hippocampal CA1 before AME or Sed. Other procedures were following Exp.1.

Results & Discussions

Exp.1: The exploration time of both object (N+F) and of each object (N or F) in the training session had no significant differences between two conditions. By contrast, DRs of AME, but not of Sed, were significantly above the chance level (50%) in the test session (one sample t‐test, p<0.05). The results show that AME after learning improves memory consolidation in the subjects achieved the same level of learning. Exp.2: As was shown in the Exp.1, there were no any differences in the exploration time of both object and of each object among all conditions in the training session. However, DRs in the test session were significantly above the chance level (50%) under the AME+Pla condition (one sample t‐test, p<0.05), but not under the other conditions. These results suggest that enhancement of memory consolidation by the AME is unaffected by Pla treatment, but is abolished by protein synthesis inhibitor, ANI, treatment.

Conclusion

Taken together, our findings support the hypothesis that AME‐induced memory consolidation mediates the action of new protein synthesis in dorsal hippocampal CA1, and provide a basis for further studying the detailed mechanisms of exercise‐induced memory consolidation.

Support or Funding Information

This work was supported in part by Grant‐in‐Aid for Young Scientists (B) (26750307).