TRANSMISSION OF IMPULSES IN PERIPHERAL NERVES TREATED WITH DI-ISOPROPYL FLUORPHOSPHATE (DFP)

Abstract

Using isolated frog and cat nerves, the action potentials of the A fibers were recorded before and after local application of the irreversible anticholines-terase, di-isopropyl fluorphosphate (DFP). DFP, like eserine base in a 0.02 M concn., blocked nerve impulses in 30-40 mins. sufficiently to cause a 70-95% decrease in the height of the action potentials recorded beyond the region of application. The portion of the nerve proximal to the block conducted normally. Eserine salicylate (0.02 M) in 2 hrs. caused no change. The eserine or DEP block was abolished by washing the nerve with Ringer soln. In the case of DFP, merely lifting the nerve out of contact with the drug abolished the block. These expts. suggested that the blocking action of DFP was not through its action as an anticholinesterase. To test this, 12 bullfrogs were taken and into each of these were injected 2 gs./km. of DFP into the ventral lymph sac. Another 12 frogs served as controls. The action potentials of the 24 control sciatic nerves and the 24 exptl. nerves showed no significant differences, either to single or to repetitive stimuli. In contrast, the cholinesterase activity of the exptl. sciatic nerves was only 2.3% of that in the control nerves. This figure is well within the limits of the standard error for the cholinesterase detns. It is concluded that nerve fibers can conduct impulses under the condition of essentially complete absence of cholinesterase activity.