Cognitive deficits in a murine model of the eosinophilia-myalgia syndrome: a preliminary report

The described study was to determine the effects of chronic exposure to 1,1'-ethylidenebis[L-tryptophan] (EBT), a tryptophan contaminant, on cognitive behavior of female C57BL/6 (C57) mice. EBT (also designated as "peak E" or "peak 97") is one of several compounds that are suspect in the eosinophilia-myalgia syndrome (EMS). Groups of female C57 mice (12/group) were injected IP with saline (SAL), tryptophan (TRY), EBT, or an EBT + tryptophan combination (EBT + TRY) over a 6-week period. Previous experiments established that the dosing conditions produce several characteristics of EMS, including dermal inflammation and fibrosis, increased dermal mast cells, and increased levels of quinolinic acid. The mice exposed to EBT + TRY were abnormal during the solution of a Morris water maze problem. First, they had a shorter latency to locate the submerged platform goal during the initial day of training compared to SAL or TRY mice; secondly, they did not show the systematic reduction in latency to locate the platform goal across days of training noted for SAL or TRY mice. These abnormalities occurred in the absence of altered body weight or gross motor activity during the treatment procedure, or in the animal's swim speeds at the time of testing, 3 days after termination of treatment. The results suggest that prolonged exposure to EBT + TRY can alter the reaction to a stressful environment and can alter cognitive behavior.