Association between low plasma tryptophan and blackouts in male alcoholic patients.

Alcohol has been observed to alter various aspects of memory function. Some of the most extreme forms of memory impairment experienced by alcoholics are blackouts. There are at present very few data on the biological mechanisms underlying alcohol-related memory impairment. A variety of mechanisms including the cholinergic and catecholaminergic systems have been implicated in learning and memory. More recently, however, the importance of the serotonergic system in memory function has been demonstrated. We investigated whether patients with a history of blackouts had lower plasma levels of the serotonin precursor tryptophan than patients without such a history. Tryptophan values were significantly lower in patients who had experienced blackouts than in patients who had not. No significant differences between the two group of patients were observed for other amino acids sharing with tryptophan the same transport carrier into the brain. Drinking history variables did not differentiate among the two patient groups. Our data suggest that a decrease in plasma tryptophan (and concomitant lowered brain serotonin) could increase the vulnerability of certain individuals to manifestations of various aspects of memory impairment including one of its most extreme forms, the blackout.