Effect of tryptophan treatment on self-biting and central nervous system serotonin metabolism in rhesus monkeys (Macaca mulatta).

Abstract

Two studies were conducted to examine the effects of oral L-tryptophan (TRP) supplementation as a treatment for self-injurious behavior (SIB) and to investigate behavior and central serotonin turnover of male rhesus monkeys. In Study One, TRP was administered to seven individually housed rhesus monkeys with a recent history of spontaneous SIB. While the monkeys were on TRP treatment (100 mg/kg twice a day), cisternal cerebrospinal fluid (CSF) concentrations of 5-hydroxyindoleacetic acid increased markedly (p = .0013) above baseline (baseline mean = 207.6 pmol/ml +/- 39; TRP mean = 320.3 pmol/ml +/- 83.4), and the duration of self-biting behavior decreased below baseline (p = .03). In Study Two, 14 individually housed rhesus monkeys without a history of SIB were placed on three different doses of TRP in random order (50, 100, and 200 mg/kg twice a day). TRP had no effect on any behavioral or biochemical variables in the normal monkeys. Supplemental tryptophan in well-tolerated doses reduced self-biting and increases serotonin turnover rate in male monkeys with a recent history of SIB. The same doses of TRP do not affect behavior or serotonin metabolism in male monkeys without a history of SIB.