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.