Dietary tryptophan modulation and aggressive behavior in mice.

The effects of a tryptophan-free diet on isolation-induced fighting and predatory cricket killing in mice were examined. The results demonstrated that consumption of a tryptophan-free diet for 18-20 days decreased both the number of fighters and duration of isolation-induced fighting; increased the number of cricket-killing mice and decreased the latencies to attack and the latencies to kill crickets; reduced brain serotonin 27%; increased water intake 38%; and decreased body weight 27% without affecting food intake. To determine if these effects were due specifically to the lack of dietary tryptophan, other groups of mice were fed a 5% tryptophan load in the standard chow; a 0.15% tryptophan supplement in the tryptophan-free diet; or a 3 grams/day restricted chow diet. The lack of tryptophan in the diet produced the marked inhibition in isolation-induced fighting, the reduction in brain serotonin, and the large decrease in body weight. The other non-specific effects appeared to be related to general factors such as dietary need for the cricket killing or diet composition (other than the lack of tryptophan) for the water intake.