Effects of chronic tryptophan loading on serotonin (5-HT) levels in neonatal rat brain

Several earlier studies reported that the acute administration of L-tryptophan to adult rats caused an increase in brain serotonin levels. This study describes the effects of chronic tryptophan loading on serotonin concentration levels in various regions of the neonatal rat brain. Rats were injected with tryptophan methyl ester hydrochloride (100 mg/kg), intraperitoneally, daily from day 4 to day 24 after birth, and sacrificed on days 8, 19, and 29 after first injection. The brains were immediately dissected into their component regions, and serotonin concentration levels were measured by a radioenzymatic method. Chronic tryptophan loading produced a significant (P < .05) decrease in serotonin levels in all the brain regions as compared with saline-treated controls, except the pons and medulla regions, which showed significant (P < .001) increase on day 8.