Duration and intensity of behavioral change after sublethal exposure to soman in rats

The behavioral effects produced by acute exposure to sublethal doses of pinacolyl methylphosphonofluoridate (soman) were examined in the Sprague Dawley rat. Two hours after exposure to soman (100-150 micrograms/kg IM), dose-related decreases in spontaneous motor activity (SMA), fore- and hindlimb grip strength, thermal sensitivity, and rectal temperature were observed. In addition, acoustic startle response amplitude decreased, while response latency increased. Soman also depressed the percentage of conditioned avoidance and escape responses and increased response latency. In both the 103 and 116 micrograms/kg dose groups, effects on hindlimb grip strength persisted up to 14 days after exposure, while effects on hot plate response lasted for 7 days. A biphasic change in motor activity was seen in the 103 and 116 mg/kg soman groups: Initial SMA depression during the first 24 hours after exposure was followed by SMA increases which persisted up to 21 days. Animals that showed delayed hyperactivity often exhibited seizures and increased excitability when handled. The results of these studies demonstrate that sublethal doses of soman can cause marked and often long-lasting changes in behavior in the rat.