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Journal of Cerebral Blood Flow and Metabolism 10:1-12 © 1990 Raven Press, Ltd., New York

A New Method to Measure Brain Serotonin Synthesis In Vivo. I. Theory and Basic Data for a Biological Model

M. Diksic, S. Nagahiro, *T. L. Sourkes, and Y. L. Yamamoto Department of Neurology and Neurosurgery, Montreal Neurological Institute and Hospital, and *Departments of Psychiatry and Biochemistry, McGill University, Montreal, Quebec, Canada

Summary: We describe here an autoradiographic method to measure the in vivo rate of serotonin synthesis in rat brain. The method is based on the use of the L-tryptophan analogue a-methyl-L-tryptophan (a-MTrp), which is con­ verted in vivo into a-methylserotonin (a-M5HT). Since a-M5HT is not a substrate for monoamine oxidase, it is accumulated in the brain tissue. Data are presented to confirm time-dependent conversion of a-MTrp into a-M5HT in the dorsal raphe nucleus and also in the pineal body, an organ outside the blood-brain barrier. It has also

been shown that washing brain slices in 10% trichloro­ acetic acid results in