Protection against both lethal and behavioral effects of soman

This work developed two drug mixtures which alone had no effect on performance of a criterion behavior but when given as a pretreatment would protect against organophosphate-induced lethality and incapacitation. Candidate drugs (alone and together) were given to rats trained to respond on a two-component Fixed Ratio 10 - Extinction (FR10-EXT) schedule. After generating dose response curves for each cholinolytic drug, mixtures of atropine (A) + mecamylamine (M) + pyridostigmine (Py) or physostigmine (Ph) were prepared and a combination of doses that produced no effects on operant performance was determined (Mix I:A = .78, M = .78, Py = .056 mg/kg; Mix II:A = .78, M = .78, Ph = .026 mg/kg). Both pretreatment mixtures provided equivalent protection against the lethal effects of the organophosphate soman; however only Mix II was capable of reversing soman-induced physical incapacitation (PI) as assessed by performance on an accelerating rotarod or FR10 responding. Pretreatment of animals with Mix II resulted in significantly higher levels of brain acetylcholinesterase (AChE) than Mix I pretreated subjects 4 hrs after 1.3 LD50 soman, although peripheral AChE levels were not different. The results indicate organophosphate-induced PI can be attenuated by pretreatment with tertiary carbamates which protect significant amounts of brain AChE from irreversible inhibition.