Pain and tryptophan.

Tryptophan, the precursor for serotonin, was given to five patients with recurrent pain and diminished sensory deficits following rhizotomy and cordotomy. Their sensory deficits for both touch and pinprick reexpanded to the maximum extent initially recorded after their operative procedures. Their pain was again relieved. No clear understanding of the mechanisms responsible for these changes can be proposed at this time. It is speculated that a metabolic modulation of neurotransmitter functions is responsible for the clinical observations.