Protocol: A physiological method to selectively decrease brain serotonin release

In this protocol the effect of both an acute and chronic tryptophan (TRP)-free diet on brain serotonin (5-HT) release was studied in rats. Extracellular levels of cortical 5-HT, assessed by in vivo microdialysis, revealed a decrease in the release of this monoamine. Indeed, 120 min after the acute administration of a TRP-free diet, cortical 5-HT release decreased significantly by about 40% with respect to a balanced diet and the decrease persisted for more than 6 h. The chronic intake of a TRP-free diet induced a gradual reduction in 5-HT release. Five days after the diet consumption, our HPLC system detected no 5-HT in cortical dialysate. On the contrary, the acute or chronic administration of the TRP-free diet made no significant change in extracellular noradrenaline content in the frontal cortex, suggesting a specific action of the diet on the serotonergic system. Therefore, the administration of a TRP-free amino acid diet offers a non-pharmacological means for effectively decreasing brain 5-HT release. This diet can be used to study the physiological and behavioral effects of reduced brain 5-HT function.