A reduction of the tone of 5-hydroxytryptamine neurons decreases utilization rates of striatal and hypothalamic enkephalins.

The administration of drugs such as fenfluramine, p-chlorophenylalanine or 5,7-dihydroxytryptamine, which lower brain 5-hydroxytryptamine content, increases the enkephalin content of hypothalamus and striatum. None of these treatments changes proenkephalin mRNA content. On the basis of these results, we propose that 5-hydroxytryptamine does not increase the biosynthesis of enkephalin, but might increase the content of the neuropeptide by reducing peptide utilization.