Spatial long-term memory is related to mossy fiber synaptogenesis

Structural synaptic changes have been suggested to underlie long-term memor y formation. In this work, we investigate if hippocampal mossy fiber synapt ogenesis induced by water maze overtraining can be related with long-term s patial memory performance. Rats were trained in a Morris water maze for one to five identical daily sessions and tested for memory retrieval 1 week an d 1 month after training. After the last test session, the rat brains were obtained and processed for Timm's staining to analyze mossy fiber projectio n. The behavioral results showed that with more training, animals showed a better performance in the memory tests, and this performance positively cor relates with Timm's staining in the stratum oriens. Furthermore, with the u se of the NMDA antagonist MK801 before, but not after acquisition, water ma ze spatial memory was impaired. Increased Timm's staining in the stratum or iens was observed in the animals treated with MK801 after acquisition but n ot in those treated before. Finally, we observed that mossy fiber synaptoge nesis occurs mainly in the septal region of the dorsal hippocampus, support ing the idea that this anterior region is important for spatial memory Alto gether, these results suggest that mossy fiber synaptogenesis can be relate d with spatial long-term memory formation.