Tryptophan deprivation: effects on mouse-killing and reactivity in the rat

Following a 5-week maintenance on a low-tryptophan diet, brain 5-HT content was reduced to 75%, whereas NA and DA levels remained unchanged as compared to controls. Reactivity to air-puffs as well as to the novelty of the open-field was increased. Incidence of mouse-killing was examined in 2 groups of Wistar rats maintained on the tryptophan-deficient diet for 2 and 4 weeks, respectively, before being tested with a mouse: 70% and 60% of them killed mice, compared to 20% killers in rats given free access to standard food, and 20% killers in rats given a limited access to standard food so as to reproduce the suppression of weight gain observed in the tryptophan-deficient animals. Prior non-aggressive interactions with mice significantly reduced later incidence of mouse-killing following a 4-week tryptophan-poor diet, thus confirming the suppressant effect of prior familiarization with mice on elicitation of mouse-killing as a result of brain 5-HT depletion. Once initiated, mouse-killing persisted even when the rats were returned to standard food, demonstrating that reduced 5-HT activity is not necessary for the maintenance of this behavior.