Tryptophan depletion selectively reduces CSF5-HT metabolites in healthy young men: results from single lumbar puncture sampling technique

Plasma tryptophan (Trp) depletion is a commonly used tool for determining t he role of brain serotonin (5-HT) function in a variety of psychiatric diso rders. This study measured the cerebrospinal fluid (CSF) monoamine metaboli te response to Trp depletion and control testing in five healthy subjects u tilizing a single lumbar puncture. Testing was done in a placebo-controlled , double-blind, randomized, cross-over design. Plasma-free and total Trp le vels and behavioural ratings were obtained prior to and 5 h after ingestion of each amino-acid drink. CSF was obtained by performing a standard lumbar puncture 7 h after ingestion of the drink. Compared to control testing, Tr p depletion caused a significant decrease of CSF 5-hydroxyindoleacetic acid (5-HIAA) (p = 0.03), but not of homovanillic acid or 3-mefhoxy-4-hydroxy-p henylglycol. Behavioural ratings were minimally affected in all subjects. T his confirms that plasma Trp depletion reduces central nervous system measu res of 5-HT function and suggests that the single lumbar puncture technique may be sufficient to detect the extent of CSF 5-HIAA. changes during Trp d epletion studies.