Long-term tryptophan administration enhances cognitive performance and increases 5HT metabolism in the hippocampus of female rats.

It has been shown in various studies that increase in serotonergic neurotransmission is associated with increased memory consolidation whereas low brain 5HT impairs memory performance. In the first phase of our study we found that tryptophan (TRP) administration for 6 weeks increased plasma TRP and whole brain TRP, 5HT and 5HIAA levels. Many brain regions are involved in the learning process but particularly the hippocampus is known to have key role in learning and memory. The present study was therefore designed to investigate the effects of TRP loading particularly on hippocampal 5HT metabolism and cognitive performance in rats. TRP-treated rats demonstrated spatial enhancement as evidenced by a significant decrease in time to find the hidden food reward in radial arm maze test (RAM). The important finding of the present study was the greater increase in the 5HT metabolism in hippocampus than in any other brain region of the TRP-treated rats. This increased 5HT metabolism in the hippocampus emphasizes the involvement of this region in memory process.