Background: Alcohol self-administration in the laboratory has been used to evaluate pharmacological treatments and neurobiological mechanisms that underlie alcohol use in alcohol-dependent individuals. This study evaluated whether attenuation of serotonin synthesis via depletion of its precursor tryptophan reduces the amount of alcohol consumed in a self-administration paradigm in non-treatment-seeking individuals with alcohol use disorders.
Methods: Individuals with alcohol dependence (n = 8) and alcohol abuse (n = 4) who were not seeking treatment were recruited by advertisement and participated in two test days, 1 week apart. Each test session was preceded by administration of a concentrated amino acid drink that resulted in a rapid and significant decline in plasma free tryptophan (active depletion) or a similar drink containing tryptophan (placebo depletion). Tests were conducted in a randomized, double-blind fashion. The test session began with a cue exposure session where subjects were exposed to their favorite alcoholic beverage and asked to rate their craving for alcohol. After this, subjects were administered a priming drink designed to raise blood alcohol levels to 0.02 g%. Subjects then had the opportunity to drink up to eight additional drinks, each designed to raise blood alcohol levels by 0.02 g%, or to receive $3 for each drink not consumed over a 2-hr period.
Results: There were no significant differences in alcohol consumed or subjective intoxication with active tryptophan depletion compared with placebo. Self-reported craving correlated with the amount of alcohol consumed in the session.
Conclusions: These data question the dependence of alcohol self-administration on the ongoing synthesis of serotonin.