Cholinesterase activity of chronic partially isolated cortex

Abstract

Partially isolated cerebral cortex gradually develops an increased susceptibility to experimentally induced epileptiform activity. Such cortex becomes supersensitive to topically applied acethlcholine and to other stimuli. The hyperexcitability of such isolated cortex appears to be due to denervation supersensitivity and possibly to the elimination of inhibitory mechanisms by undercutting. The hydrolysis rates of acetylcholine, acetyl-[beta]-methycholine, and butyrylcholine by homogenized monkey cerebral cortex indicates greater amounts of specific acetyl-cholinesterase are contained in this tissue than nonspecific butyryl-cholinesterase. Associated with isolation of the left frontal area there is a significant decrease in the acetylcholine hydrolyzing ability of the left frontal and pre- and postcentral homogenized areas. Acetyl-[beta]-methylcholine hydrolysis by the left frontal and precentral areas is also decreased. Butyrylcholine is hydrolyzed at the control rate in all cortical areas of brains containing a frontal isolation. Control cortical slices from the various cerebral areas hydrolyze acetylcholine at a rate of 41 to 73% that of the corresponding homogenized tissue. Slices from brains containing left frontal isolation hydrolyze acetylcholine at a rate 56 to 106% that of the corresponding homogenized tissue. The increased permeability of the slices to acetylcholine is most marked in the isolated left frontal area and in the adjacent precentral area. Chronic partially isolated cerebral cortex shows a complete loss of the permeability barrier to acetylcholine and a marked decreased cholinesterase activity (50 to 60%). These two factors may contribute to the neuronal hypoexcitability and supersensitivity to acetylcholine line of chronic partially isolated (denervated cerebral cortex.