Effects of Organophosphate Nerve Agents on Visual Cortical Function

摘要

The effects of the anticholinesterase agents pyridostigmine and diisopropylfluorophosphate (DFP) on the visual evoked potential (VEP) were examined using phase-reversed sine wave gratings of varying spatial and temporal frequencies and contrasts. Response amplitudes and noise levels were determined by Fourier transforming the VEP and summing the first 15 even and odd harmonics, respectively. Both agents caused a depression of the VEP in a dose-dependent fashion across all spatial frequencies in 50% of the trials and low frequencies in the remaining trials. Responses to low temporal frequencies were depressed, and high frequencies were enhanced. Studies in which contrast was varied showed that VEP depression resulted from a decrease in the response system gain rather than a change in the contrast sensitivity. Administration of DFP also depressed the VEP equally across all spatial frequencies in the majority of animals and depressed low spatial frequencies in the remaining 25%. The VEP depression stemmed mainly from a reduction in system gain rather than from a change in contrast sensitivity. DFP had a proportionally greater influence on contrast sensitivity than that of pyridostigmine. Of 13 cells in which physostigime was applied iontophoretically, 2 showed no changes in firing rate, while 7 were enhanced and 4 were depressed by the drug.