The regional rate of serotonin synthesis estimated by the alpha-methyl-tryptophan method in rat brain from a single time point

A simplified approach to the measurement of the rate of serotonin (5-HT) synthesis in laboratory animals is presented using autoradiography and labeled alpha-methyl-L-tryptophan. The method is based on the assumption that the volume of distribution of an apparent precursor pool is the same in all brain structures. The apparent distribution volume (Vapp) of the tracer was estimated from our previous data and found to be 0.45 +/- 0.1 ml g-1 (n = 147) as an average in all brain structures. When this value of Vapp was used, the rates of 5-HT synthesis in the rat brain structures, calculated from the single time point method, were not significantly different from those calculated by the dual time point method, where both Vapp and K* were estimated. The rates from the two approaches did not differ when compared by analysis of variance (p > 0.8), Mann-Whitney rank sum test (p > 0.11), Bonferroni-corrected two-tailed t test, or when the ratio between two groups was tested against the hypothesis of being 1. The agreement between rates of 5-HT synthesis estimated by the two methods was very good, suggesting that the simplified method proposed here is appropriate for these kind of measurements.