AMINO ACID AND PROTEIN METABOLISM OF THE BRAIN‐VII 1 THE PENETRATION OF CHOLINESTERASE INHIBITORS INTO THE NERVOUS SYSTEM OF THE FROG

I N THE course of our studies of cetebral protein metabolism (LAJTHA el a/., 1957; FURST et a/., 1958) the incorporation of r4C]lysine into the proteins of succeeding segments of the sciatic plexus and nerve of the frog was investigated (WAELSCH, 1958; LAJTHA, 1961). It was found that a proximal-distal gradient of specific activity of protein bound lysine developed in time, a gradient which reversed itself after several weeks, the specific activity of the protein bound lysine of the most distal nerve segment being equal to or higher than that of the proximal segments of the nerve and plexus. This finding aroused our interest in the question whether or not the gradient of radioactivity observed is an indication of synthesis of the axonal protein in the perikaryon of the respective nerve cells and transportation distally by axonal flow. In order to extend these studies by measurement of a parameter other than incorporation of an isotopic amino acid, the distribution, and recovery after inhibition, of the total cholinesterases (substrate : acetylcholine) and also of pseudo cholinesterase (butyryl choline) and true or acetyl cholinesterase (acetyl /3-methylcholine) were investigated, since changes in enzyme activity may tentatively be taken as a measure of the synthesis or breakdown of the enzyme protein. Such a study by itself or when combined with isotope experiments might provide information as to the origin of the esterases of peripheral nerve, and whether they are synthesized in the cell body and transported in the nerve fibre to the nerve ending or synthesized locally in the fibre itself. Preliminary to such an investigation, the knowledge of the time sequence of inhibition of the enzymes is essential. Therefore, the relative rates of penetration of inhibitors from the cerebrospinal fluid and from blood into peripheral nerve were examined by use of two related compounds with approximately equal in oitro cholinesterase inhibitory activity, one an ionized quaternary ammonium compound, the other a lipophilic tertiary amine. The cholinesterase inhibitors were injected either into the subcutaneous lymph sac or into the fourth ventricle of the brain of the frog, and the levels of pseudo and true cholinesterases in brain, spinal cord and nerve were determined at various times to establish the sequence of inhibition, and the route by which the