AN ELECTROPHYSIOLOGICAL AND HISTOLOGICAL STUDY OF TRYPSIN INDUCED DEMYELINATION

Ten-mu l quantities of trypsin or saline were injected into rat tibial nerve and the physiological and histological changes evaluated and co mpared to the focal demyelinating lesions induced by intraneural injec tion of rabbit EAN serum and proteinase K. The injection of trypsin pr oduced progressive conduction block that was maximal on day 4, and a s lowing of motor nerve conduction. Early retraction of myelin at parano des, vesicular change, and macrophage stripping of myelin from nerve a xons were seen on histological examination. At day 4, the first groups of completely demyelinated axons were seen, typically in a perivascul ar distribution. These changes were similar to those seen in the posit ive controls and thus support the postulate that proteolytic enzymes f rom macrophages - the dominant cellular species within the demyelinati ng lesion, play a central role in degradation of the myelin sheath in demyelinating diseases.