George G. Karas

Dieldrin exposure and vigilance behavior in sheep

Sheep exposed to a daily oral dose of 20 mg dieldrin per kg body weight exhibited a large decrement in the performance of a vigilance task. Three of four sheep recovered their preexposure response levels within 10 days following the termination of exposure. Reexposure of these three animals to 5 mg dieldrin per kg body weight also resulted in a response decrement.

AVOIDANCE LEARNING IN SWINE

The purpose of the present study was to develop a measure of learning in swine that could be mzde rapidly and would be sensitive to individual differences, so that the genetic effects of irradiation on this measure of learning could be investigated. Pxevious learning studies with swine (Hafez, et al., 1962) used procedures not amenable to testing the large numbers of Ss necessary for genetic analysis. Therefore, avoidance learning, typified by the work of Solomon (1953) with dogs and Mowrer (1946) with rats, was chosen since a response indicative of learning could be obtained in a relatively few trials of a short, near constant length. The performance of swine was tested in 40 trials under three different spacings: consecutively (40 X 1 ), 20 per day (20 X 2 ) , and 10 per day (10 X 4 ) . Although spacing would be expected to increase performance, more Ss could be tested under massed training. If the latter approached spaced training in sensitivity to individual differences, it would be preferable. Sensitivity to individual differences was defined as maximum when the average percentage of avoidances for a set of trials was 50%, since the variance of binomial data is maximum when p = q = 1/2.

PERFORMANCE ON A VIGILANCE TASK UNDER CONDITIONS OF TRUE AND FALSE KNOWLEDGE OF RESULTS

A vigilance study comparing the effects of true and false knowledge of results is presented. The study determines at what point, if any, the effects of false knowledge of results (FKR) reflect the results of earlier vigilance studies involving true knowledge of results (KR). The task used required a response to a signal on a display panel. The KR was either true or randomly generated FKR. Latency of response was the dependent variable. The results demonstrated that groups receiving KR do not differ significantly in performance from groups receiving FKR. The best results were obtained at the 100% feedback level, a drop occurred at the 50% level, and the hypothesized drop in performance occurred between 30% and 20%.

Dieldrin toxicity and successive discrimination 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.

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 monkeys tonereporting behavior during hearing threshold testing.

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 μg/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 μg/100 ml during gestation when tested on nonspatial, two-choice visual discrimination problems at 10–15 months of age.

EFFECT OF DIELDRIN EXPOSURE ON DETOUR BEHAVIOR IN SHEEP

Two experiments were conducted to investigate the effect of a chlorinated hydrocarbon insecticide (dieldrin) on detour behavior in sheep. The visibility of the goal object and its distance behind the barrier were also studied. Dieldrin exposure did not significantly affect detour behavior. The distance of the goal object from the barrier, and the visibility of the goal object produced no reliable differences.

Acquisition of a jumping avoidance response in hamsters

Hamsters were found to readily acquire a jumping avoidance response, but showed no differential performance as a result of differences in shock intensity or intertrial interval. The performance of rats in an earlier experiment was superior to that of the hamsters in our study.