Effects of subchronic administration of soman on acquisition of avoidance-escape behavior by laboratory rats

Holtzman male Sprague-Dawley rats were given four injections of saline or soman at 31 micrograms/kg or 46 micrograms/kg. The injections were given every 3 days during a 2-week period. Tail vein blood samples, drawn 24 hr before the first injection and 24 hr after the last injection, were analyzed for acetylcholinesterase (AChE) inhibition. For the low and high soman groups, whole blood AChE was inhibited 20 and 24%, respectively, while plasma AChE was inhibited 17 and 25%, respectively. Parallel saline injections produced a small inhibition of whole blood AChE and an increase in activity (negative inhibition) of plasma AChE. During the second week of soman administration rats began training on a discriminated shock avoidance task. The seven animals administered 46 micrograms/kg soman did not learn the lever-pressing avoidance response during a period of 120 days. Five of eight saline rats and four of seven 31 micrograms/kg soman rats learned the avoidance response. There was no significant difference between learners relative to rate of learning of the avoidance task. All of the rats learned to escape the shocks. These data indicate that subchronic soman inhibits learning of new behaviors by laboratory rats.