Effect of L-tryptophan pretreatment on d-amphetamine self administration.

Pretreatment with doses of the amino acid, L-tryptophan, known to increase brain serotonin levels, markedly reduced the number of intravenous self-injections of d-amphetamine in rats previously demonstrating stable self-administration patterns. This attenuation of response was dose dependent in both magnitude and duration. Pretreatment with L-tryptophan did not alter the response rate in animals trained on an FR-40 food reinforced paradigm. L-tryptophan administration did not alter the apparent turnover of dopamine in nucleus accumbens septi, important since manipulation of dopamine in this brain area exerts a marked influence on psychomotor stimulant self-administration. These results are consistent with previous reports suggesting a role of serotonergic neurons in the self-administration of d-amphetamine.