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Tryptophan depletion during continuous CSF sampling in healthy human subjects
L L Carpenter1, G M Anderson, G H Pelton
1Butler Hospital, Department of Psychiatry and Human Behavior, Brown University School of Medicine, Providence, RI 02906, USA.
Summary
Tryptophan depletion significantly lowered plasma and cerebrospinal fluid tryptophan. This suggests reduced serotonin turnover in the brain, impacting mood and behavior research.
Area of Science:
- Neuroscience
- Biochemistry
Background:
- The tryptophan depletion paradigm is used to study mood and behavior by lowering serotonin.
- This method assumes a decrease in brain serotonin (5-HT) levels corresponds to lowered plasma tryptophan (TRP).
Purpose of the Study:
- To verify if central TRP and 5-HT levels decrease during standard TRP depletion in healthy adults.
- To measure changes in cerebrospinal fluid (CSF) TRP and 5-HIAA, a 5-HT metabolite.
Main Methods:
- Healthy adults consumed a low-TRP diet and TRP-free amino acid drink.
- Continuous CSF sampling via lumbar catheter for 13.5 hours.
- Simultaneous plasma sampling to correlate central and peripheral TRP levels.
Main Results:
- CSF TRP and plasma TRP levels significantly decreased (92% and 85% respectively).
- CSF TRP nadirs occurred hours after plasma nadirs.
- CSF 5-HIAA showed a modest decrease (mean 31%), with levels lowest 8-12 hours post-drink.
Conclusions:
- TRP depletion effectively lowers central TRP levels.
- The method leads to a notable reduction in central serotonin turnover, supporting its use in mood and behavior studies.