Behavioral decrements persist in rhesus monkeys trained on a serial probe recognition task despite protection against soman lethality by butyrylcholinesterase.

Recently, it has been demonstrated that an exogenously administered enzyme such as butyrylcholinesterase (BuChE) can prevent death in rhesus monkeys exposed to multiple-lethal doses of the acetylcholinesterase inhibitor soman when the enzyme is given prior to soman exposure (3). We report that despite BuChE protecting against soman-induced lethality, behavioral effects are seen in these monkeys which last for at least 6 days as measured by performance on a serial probe recognition (SPR) task. Analyses of the serial position curves showed that performance was lower on the probe trials when the probe items were from the middle of the list than when the probe items were from the beginning or end of the list which were unaffected. BuChE given alone also produced behavioral effects, causing all animals not to respond on the probe trials until 8 h following BuChE administration. Taken together, these findings suggest that the BuChE is not completely binding all of the soman and that a concentration of soman which is capable of causing behavioral effects may be entering the CNS.