Determination of serotonin turnover in the rat brain using 6-fluorotryptophan.

After intraperitoneal injection of rats with 6-fluorotryptophan (6-FT), brain 5-hydroxytryptamine (5-HT) levels decreased exponentially over 1 h. Depletion was dose-dependent and maximum depletion was observed at 200 mg/kg. 6-FT (200 mg/kg) did not significantly alter the content of 5-hydroxyindoleacetic acid. Turnover rates of 5-HT obtained by the 6-FT and other methods were fairly consistent. 6-FT had little effect on the content of noradrenaline and dopamine. These data suggest that 6-FT completely inhibits tryptophan hydroxylase, in vivo, without affecting the release of 5-HT from 5-HT neurons and with little effect on the activities of tyrosine hydroxylase. Therefore, 6-FT is a good pharmacological tool for studying the turnover rate of 5-HT in the brain.