Chromatogram obtained by performing high performance liquid chromatography (HPLC). This chromatogram profiles increasing concentration of monoamine neurotransmitters and metabolites. Specifically, shown here (from left to right) are norepinephrine, DOPAC (a dopamine metabolite), dopamine itself, 5-HIAA (a serotonin metabolite), HVA (another dopamine metabolite), and serotonin.