Predatory aggression in the mink (Mustela vison): Roles of serotonin and food satiation

5‐Hydroxytrypotophan at a dose of 50 mg/kg intraperitoneally (i.p.) sharply increased neural serotonin (5‐HT) levels in mink and considerably inhibited that animal's predatory attack on rats. Intraperitoneal injection of 5‐HT (10 and 20 mg/kg) did not influence such rat‐killing. Neural levels of 5‐HT or 5‐hydroxyindoleacetic acid (5‐HIAA) and subsequent aggression by the predator did not change to any great degree after ingestion of a single meal. Abundance of natural mink food for 3 days was associated with an increased level of 5‐HIAA in the lateral hypothalamus and the amygdala as well as with an increased latency to attack and to kill rats. 5‐HT seems to represent an endogenous factor that inhibits predatory attack by the mink; this effect appears to function through increased metabolism of 5‐HT in some brain regions, which is evident after abundant intake of tryptophan with the natural diet.