ARTICLE NO. FA962269 Subchronic Neurotoxicity Screening Studies with Six Organophosphate Insecticides: An Assessment of Behavior and Morphology Relative to

fon, and tebupirimphos were screened for neurotoxic potential, in accordance with U.S. EPA (FIFRA) requirements. Each organo-phosphate was administered through the diet for 13 weeks to separate groups of Fischer 344 rats at four dose levels, including a vehicle control. For each study, 12 rats/sex/dietary level were tested using a functional observational battery (FOB), automated measures of activity (figure-8 maze), and detailed clinical observa-tions, with half of the animals perfused at term for microscopic examination of neural and muscle tissues. Separate groups of satel-lite animals (6/sex/dietary level) were used to measure the effect of each treatment on plasma, erythrocyte (RBC), and brain cholin-esterase (ChE) activity. The results show that measures of ChE activity were consistently the most sensitive indices of exposure and assisted in the interpretation of findings. All treatment-related neurobehavioral findings were ascribed to cholinergic toxicity, oc