An acute exposure to a sub-lethal dose of soman triggers anxiety-related behavior in guinea pigs: Interactions with acute restraint

In this study, we tested the hypothesis that a single exposure of guinea pigs to sub-lethal doses of soman triggers anxiety-related behavior that is modifiable by acute stress. Prepubertal male guinea pigs were subjected to one of the following treatments: (i) saline (0.5 ml/kg, sc), (ii) soman (0.6× or 0.8×LD50, sc), (iii) saline followed 30 min later by 2-h restraint, or (iv) soman followed 30 min later by 2-h restraint. Behavior of the animals was examined 2 and 3 months later in a large open field and in the elevated plus maze. Animals that had been exposed to restraint stress alone or soman alone showed decreased exploratory activity when tested in the open field with bare floor at light intensity of 20–30 lx. Total distance traveled and distance traveled in the center of the field were shorter for animals that were exposed to either restraint stress or soman than for saline-injected animals. In addition, animals challenged with soman or restraint stress remained immobile for a longer time in the open field than did saline-injected guinea pigs. Performance in the elevated plus maze test revealed that exposure of guinea pigs to soman or restraint stress decreased their number of entries and the time spent in the open arms of the maze (measures of anxiety) and reduced their overall locomotor activity. Soman exposure and restraint stress cancelled out each other's effect on locomotion, while only attenuating one another's effect on anxiety-related behavior. It is concluded that a single exposure to sub-lethal doses of soman triggers long-lasting anxiogenesis and decreased locomotor activity and that acute restraint stress modifies the magnitude of these effects.