Abstract
Abstract— 5‐Hydroxy‐l‐tryptophan decarboxylase (EC 4.1.1.28) activity was measured in discrete regions of the rat brain by means of a sensitive micromethod lhat allows the quantitation of enzyme activity in μg amounts of brain tissue.A good correlation was obtained between serotonin levels and 5‐hydroxy‐l‐tryptophan decarboxylase activity in all the brain regions examined. Wide differences in enzyme activity were found in the different brain nuclei, with a 20‐fold difference in activity between the most active region (the nucleus raphe dorsalis) and the least active regions (the corpus callosum and the optic tract).