An investigation of the effects of l-methionine and related metabolites on rat behavior

l-Methionine, l-methionine plus l-serine, l-cysteine, l-serine, and betaine were tested on a modified discriminated Sidman avoidance schedule in rats. Daily injections of 250 mg/kg of these compounds were administered for at least 28 consecutive days. Schedule performance in the rat was monitored during this period and compared to preinjection saline controls. The results indicated that only methionine had significant behavior-disrupting effects. The disruption was removed by the addition of serine, suggesting that the methionine disrupting effect may have been due to one of the metabolites of methionine—homocysteine.