Effects of subchronic soman on avoidance-escape behavior and cholinesterase activities

Abstract

Male Sprague-Dawley rats were trained on a discriminated avoidance-escape task. They were administered subchronically saline, 12.7 μg/kg (0.125 LD₅₀) soman, or 25.5 μg/kg (0.25 LD₅₀) soman. Injections were given 5 days per week for 4 weeks. Injections were given subcutaneously immediately following the avoidance behavior test session. Soman produced a reduction in avoidance behavior efficiency in a dose dependent manner. When soman was discontinued, the rats recovered their pre-soman control baselines. Untrained rats given soman according to the same soman regimen were used to measure acetylcholine in brain and cholinesterase activities in brain, blood, and diaphragm. After 18 soman injections at 12.7 and 25.5 μg/kg acetylcholine was reduced significantly only in the amygdala. Blood cholinesterase was inhibited as much as 57% after 12.7 μg/kg soman and 74% after 25.5 μg/kg. Plasma cholinesterase was inhibited to 24% by the 12.7 μg/kg dose of soman and to 38% by the 25.5 μg/kg dose. Plasma cholinesterase recovered to control levels 11 days after cessation of soman, and whole blood cholinesterase recovered 25 days after cessation of the higher soman dose. Cholinesterase was inhibited significantly in the hippocampus and amygdala in a dose dependent manner. The cholinesterase activities appear to parallel the soman induced decrement in avoidance behavior and the subsequent recovery to control levels following withdrawal of soman.