Tryptophan and 5-hydroxyindoles in different CNS regions following acute morphine

Morphine induces naloxone-reversible increases of tryptophan and 5-hydroxyindoles in rat cerebral hemispheres, thalamus and cerebellum, but does not do so in striatum, hypothalamus, hippocampus and brain stem. Morphine also induces a rise in spinal cord 5-HIAA which is antagonized by naloxone, but there is no parallel change in tryptophan. Increases in brain 5-hydroxyindoles may be related to greater availability of tryptophan, but the elevation in spinal cord 5-HIAA appears to be unrelated to precursor availability.