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-H T) synthesis in laboratory animals is presented using autoradiography and labeled alpha-methyl-L-tryptophan. The method is based on the assu mption that the volume of distribution of an apparent precursor pool i s the same in all brain structures. The apparent distribution volume ( V-app) 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 structu res. When this value of V-app was used, the rates of 5-HT synthesis in the rat brain structures, calculated from the single time point metho d, were not significantly different from those calculated by the dual time point method, where both V-app and K- were estimated. The rates from the two approaches did not differ when compared by analysis of va riance (p > 0.8), Mann-Whitney rank sum test (p > 0.11), Bonferroni-co rrected two-tailed t test, or when the ratio between two groups was te sted 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 kin d of measurements.