“Systemic administration of the 5-HT precursor, 5-hydroxytryptophan and the monoamine oxidase inhibitor, pargyline , significantly increased the concentration of 5-HT in the pial vessels; in contrast, two depleting agents (p-chloroamphetamine and reserpine) and the tryptophan hydroxylase inhibitor, p-chlorophenylalanine, all decreased the perivascular 5-HT levels.”