An irreversible anticholinesterase probe for studying increased permeability of the rat blood-brain barrier

Phospholine iodide, a potent anticholinesterase quarternary salt, was found to be a useful probe in studying changes in blood-brain barrier permeability in rats exposed to various insults. Based on brain acetylcholinesterase (AChE) activity measurements, it was concluded that phospholine iodide, injected i.m. at a dose of 65 μg/kg, inhibited brain AChE activity in three different regions, provided that the blood-brain barrier integrity was damaged by exposing rats to osmotic shock (glycerol), convulsions (metrazole), or γ-irradiation. Enzyme activity was not inhibited in sham-handled controls treated with phospholine iodide. Possible complication from blood contamination during brain processing was ruled out. It was suggested that phospholine iodide can be used as a semi-quantitative probe to detect an increase in blood-brain barrier permeability by the establishment of a unidirectional flow of the marker from brain capillaries into extravascular spaces and the phosphorylation of brain AChE. Based on the stability of the inhibited AChE and its 100 per cent reactivability in the presence of specific nucleophiles, this probe may be useful for the study of blood-brain barrier resistance in conscious, freely moving rats exposed to various stresses.