STUDIES ON THE MECHANISM OF DEMYELINATION: MYELIN AUTOLYSIS IN NORMAL AND EDEMATOUS CNS TISSUE

— The effects on myelin of autolysis in situ after death and after purification were studied in normal brains and spinal cords and in those made edematous as a result of chronic triethyl tin (TET) feeding. Myelin prepared from normal and edematous brains and spinal cords autolyzed for 12 h at 4°C contained only slightly less basic protein than that prepared from freshly killed animals. The amounts of a light lipid‐protein fraction (dissociated myelin) usually obtained during purification of myelin from edematous CNS were about the same in tissue from freshly killed rats and those autolyzed for 12 h at 4°C. Autolysis for 12 h at room temperature resulted in formation of large amounts of dissociated myelin and loss of basic protein, but more dissociation and basic protein loss occurred in CNS from edematous brains and spinal cords than from the normal. Purified myelin prepared from freshly‐killed normal and TET‐fed rats was incubated at 37°C in media of several ionic strengths. In Krebs‐Ringer bicarbonate (physiological extracellular fluid) extensive dissociation of myelin occurred with much less in 0.04 M‐Tris buffer, pH 7.2, and only small amounts were formed in 0.01 M‐Tris. In all cases myelin from edematous CNS formed more dissociated fraction than did the normal myelin. Basic protein loss was also proportional to the ionic strength of the media, but there was no difference in loss between normal and TET‐myelin. Two different factors, proteolysis and physical extraction of basic protein by salt solutions, may be contributing to myelin dissociation and loss of basic protein.