Auditory detection behavior in parathion-treated squirrel monkeys ( Saimiri sciureus)

Effect of the organophosphorus insecticide parathion on auditory detection behavior in squirrel monkeys ( Saimiri sciureus) was investigated. Eight male squirrel monkeys were assigned to two groups and systematically exposed to daily oral doses of technical parathion. There were four monkeys in the control group and four in the 0.1-mg/kg group. The exposure period was 148 days. The control group received placebos for the entire 148 days. Prior to dosage assignment the monkeys were adapted to the laboratory and trained to bar-press in response to a 0.1-sec tone for hearing threshold testing. Daily threshold testing employed the method of constant stimuli. Hearing thresholds were determined at 500, 1000, 2000, 4000, 8000, and 16,000 Hz. Parathion exposure began after the eight monkeys were divided into two, four-animal statistically matched groups based on stable baseline hearing threshold data. An analysis of variance was performed on hearing thresholds and standard deviations of hearing thresholds. The parathion-exposed group showed a significant ( p < 0.025) increase in the standard deviation of hearing thresholds after 40 days of parathion exposure. The magnitude of the standard deviation continued to grow for 54 additional days and thereafter declined. Mean hearing thresholds between the control and exposed groups did not vary significantly. It was concluded that daily oral doses of parathion at 0.1 mg/kg caused a decrement in the squirrel monkey's tonereporting behavior during hearing threshold testing.