Development of behavioral tests for the assessment of neurologic effects of lead in sheep.

Reports of neurologic impairment of children following recovery from acute lead encephalopathy have raised questions concerning the effects of chronic low-level lead exposure on the central nervous system. Behavioral toxicologic techniques have been employed to assess the effects of lead on the central nervous system in sheep. Mature sheep receiving daily doses of 100 mg lead/kg showed a significant decrease in performance on an auditory signal detection task. Daily oral doses of 120 and 230 mg lead/sheep for 27 weeks did not alter the performance of mature sheep on a fixed-interval schedule of reinforcement behavioral task. Prenatal exposure to maternal blood lead levels of 16 or 34 mug/100 ml during gestation and postnatal daily ingestion of 16, 8, 4, or 2 mg lead/kg did not alter performance of lambs on a closed-field maze task. Slowed learning was demonstrated in lambs prenatally exposed to maternal blood lead levels of 34 mug/100 ml during gestation when tested on nonspatial, two-choice visual discrimination problems at 10-15 months of age.

Deldrin toxicity and successive discrimation reversal in squirrel monkeys (Saimiri sciureus).

Seven squirrel monkeys were systematically exposed to dieldrin (C12H10DC16) at two oral doses: 0.10 and 0.01 mg/kg-day. Two zero-dose controls were included. After 55 days of exposure dose assignments were shifted and continued for an additional 54 days. The higher dose group was shifted to zero exposure and lower dose group was shifted to high-dose exposure. Controls continued at zero exposure. The monkeys were presented with a visual nonspatial successive discrimination reversal task. During the first 55 days (preshift), control and low-dose monkeys learned the task; high-dose monkeys did not (p less than 0.001). During the subsequent 54 days (postshift), all groups performances remained at the approximate level achieved at the end of the preshift period. It was concluded that the high dose disrupted learning acquisition. This effect is speculated to be attributed to disruption of hippocampal activity. The low dose had no effect on task acquisition or maintenance.