Effects of a peripherally active carbamate (pyridostigmine bromide) an
d a centrally active organophosphate (OP) nerve agent (soman) on perfo
rmance by rhesus monkeys of a compensatory tracking (primate equilibri
um platform, or PEP) task were measured using a balanced Latin-square
design to determine the ED50 for pyridostigmine (0.66 mg/kg) and the u
p-and-down (titration) method to determine the ED50 for soman (2.50 mu
g/kg). We concluded that the PEP performance model is a sensitive and
reliable indicator of anticholinesterase (anti-ChE) behavioral toxici
ty. We also found that soman, an irreversible inhibitor of acetylcholi
nesterase (AChE), is more than 100 times more behaviorally disruptive
than the reversible peripheral inhibitor pyridostigmine, as indicated
by the difference in ED50 doses expressed in molar terms. Soman's beha
vioral toxicity is severe at levels of serum cholinesterase inhibition
(70-80%) at which pyridostigmine does not significantly affect perfor
mance. As a prophylactic treatment for OP agent poisoning, pyridostigm
ine has a substantial safety factor, since behavioral toxicity becomes
significant only at approximately four times the proposed therapeutic
dose. (C) 1994 Academic Press, Inc.