Dose-dependent effects of tryptophan on learning and memory

Abstract

The concentration of 5-hydroxytryptamine (5-HT, Serotonin) varies as a result of physiological changes in the availability of its precursor tryptophan to the serotonergic neurons in the brain. Increase in brain tryptophan occurs following an increase in plasma tryptophan concentration. Tryptophan intake increases brain serotonin metabolism and enhances memory. The Present study was designed to investigate the effects of oral administration of tryptophan (TRP) at different doses (100, 300 and 500mg/kg) for two weeks on learning and memory functions and Neurochemical changes in rats. Control rats were given drinking water. Assessment of memory in rats was done by using the water Maze. on the 14th day trail training of water Maze was given to rats and after 1h of this 2nd trial of these rats were done. On the next day (After 24h of trail) long-term memories of these rats were monitored. After 1 hour of this all rats were killed by decapitation using guillotine. Brain and blood was collected and stored at -70o C. Neurochemical estimations of Plasma and brain tryptophan, 5-HT and 5-HIAA in brain were made by HPLC-EC. Result showed that administration of tryptophan enhanced performance on water Maze test. Tryptophan treated animals exhibited higher level of Plasma as well as brain tryptophan. 5-HT and 5-HIAA levels were also increased in tryptophan treated rats. Findings are discussed in context with the role of 5-HT metabolism in learning and memory process in rats. Results may help to understand the 5-HT changes following long term TRP administration in a dose dependent manner and will help to suggest the use of TRP in serotonin related illnesses.