Effect of soman exposure on the acquisition of an operant alternation task

Following recovery from soman administration, rats were trained on an operant alternation task with a time-out between response periods. As animals became proficient at the task, both the operant requirements and the length of time-out periods were gradually raised to Fixed Ratio 20 with a 20-second Intertrial Interval. Training sessions continued until animals attained criterion or 100 training sessions had been given. Soman produced a dose-related lethality and signs of cholinergic hyperstimulation. Although all saline controls and 90% of animals receiving 75 micrograms/kg soman attained terminal performance, only one-third of the animals given either 85 or 95 micrograms/kg soman were able to learn this task. Sessions to attain criterion performance produced similar dose-dependent results: All saline animals attained criterion, while only 60%, 33% and 33% of the animals given 75, 85 or 95 micrograms/kg soman respectively reached criterion. Additionally, both 85 and 95 micrograms/kg soman produced severe neural lesions, including cortical atrophy and ventricular dilation.