Some problems in interpreting the behavioral effects of lead and methylmercury

Two sets of observations are reported as illustrations of problems encountered in behavioral toxicology. First, in an attempt to determine the contribution of methylmercury-induced ataxia to behavioral changes observed on the fixed-consecutive-number schedule, some ancillary control experiments were undertaken. Neither pharmacologically-produced incoordination (ethanol) nor mechanically-produced incoordination (foot taping) led to behavioral changes similar to those seen after exposure to methylmercury. Second, total crop impaction in a pigeon that died during a behavioral experiment on lead suggested some further work. Lead-induced crop stasis in pigeons was measured by x-raying the passage of force-fed stainless steel ball bearings through the crop. This retardation of motility reliably preceded signs of overt toxicity. These results suggest that the behavioral changes in the pigeon noted by us and reported by other investigators cannot be attributed to CNS dysfunction alone, but more likely arise from starvation, or from combined CNS damage and starvation. In addition, these results demonstrate that the appearance of behavioral effects prior to overt toxicity does not necessarily reflect CNS damage.