Simultaneous determination of 3, 4?dihydroxyphenylalanine, 5?hydroxytryptophan, dopamine, 4?hydroxy?3?methoxyphenylalanine, norepinephrine, 3, 4?dihydroxyphenylacetic acid, homovanillic acid, serotonin, and 5?hydroxyindoleacetic acid in rat cerebrospinal fluid and brain by high?performance liquid chromatography with electrochemical detection.