Relationship of brain tryptophan and serotonin in improving cognitive performance in rats

Brain function can be affected by the availability of dietary precursors of neurotransmitters. The diet induced increase in tryptophan (TRP) availability has been shown to increase brain serotonin synthesis and various related behaviors. Evidence shows that TRP and serotonin (5HT; 5 Hydroxytryptamine) play a significant role in memory function. Enhanced brain serotonin activity has been shown to improve cognitive performance in animals and human whereas decreasing brain 5HT levels by acute TRP depletion has been shown to impair cognition. A number of methods have been used for the assessment of memory in animals. In the present study, the radial arm maze and the passive avoidance was used for the assessment of memory in rats following long-term TRP administration. TRP at doses of 50 and 100 mg/kg body weight was orally administered for 6 weeks. The present study shows a significant improvement in memory of rats following both doses of tryptophan. Plasma TRP, brain TRP, 5HT and 5 hydroxy indol acetic acid (5HIAA) levels were increased significantly following administration of TRP. The results of the present study suggest that increase in brain 5HT metabolism following long term TRP administration may be involved in enhancement of memory.