Effects of l-dopa administration on the serotonergic system in rat brain: Correlation between levels of l-dopa accumulated in the brain and depletion of serotonin and tryptophan

Abstract

Following administration of an acute dose of l-dopa (200 mg/kg i.p.), the concentration of this aminoacid increased rapidly in whole rat brain, to 10 μg/g and this new level was maintained for at least 20 min. At the same time, there was a significant ( p < 0.01) depletion of brain serotonin (5HT), which was correlated with the level of dopa in the brain. The level of brain tryptophan (TP) also decreased. If l-dopa was given orally at a dose of 250 mg/kg, an increased concentration of this drug in the brain was still seen but the levels reached were 20 times less than the levels obtained after i.p. administration. In this situation the brain levels of 5HT and TP were unchanged. The chronic administration of l-dopa did not cause accumulation of the drug in the brain nor did it affect the concentration of 5HT and TP.