Effects of dietary supplements and a tryptophan-free diet on aggressive behavior in rats.

The effects of dietary excesses of tryptophan, histidine, tyrosine or choline and of a tryptophan-free diet were examined on shock-induced fighting, muricide and jump-flinch thresholds. Following the tryptophan-free diet, shock-induced fighting and pain sensitivity were specifically increased. The increased incidence of muricide was not specific to the lack of tryptophan in the diet. Groups of rats which were pair fed chow or had 0.15% L-tryptophan added to the tryptophan-free diet increased muricide as well. Brain 5-HT levels were 41% depleted following the tryptophan-free diet and reduced 13% with the 0.15% tryptophan supplement. In addition body weights were reduced in the three groups compared to control. None of the excess diets affected shock-induced fighting, muricide and jump-flinch thresholds. Body weights were decreased in the excess tryptophan, histidine, tyrosine and choline groups. These data indicate that the expression of different forms of aggression appears to be influenced by a tryptophan deficiency in the diet, but not by excesses of tryptophan, tyrosine, histidine and choline.