CHANGES IN THE DISTRIBUTION OF A CALCIUM-DEPENDENT ATPASE DURING DEMYELINATION AND REMYELINATION IN THE CENTRAL-NERVOUS-SYSTEM

A calcium-adenosine triphosphatase (Ca2+-ATPase) activity expressed by CNS nerve fibres has been examined during demyelination and remyelina tion in rats, 21-26 days after an intraspinal injection of ethidium br omide. The Ca2+-ATPase distribution was determined cytochemically, usi ng a technique believed primarily to reflect the presence of ecto-ATPa ses. We confirm that in normal nerve fibres Ca2+-ATPase activity was p resent on the external surface of the myelin sheath, and on the axolem ma at the nodes of Ranvier. Labelling of the internodal axolemma was r estricted to small, scattered, punctate regions. However, following de myelination the Ca2+-ATPase activity was expressed continuously along both the exposed, previously internodal axolemma of entirely naked axo ns, and it was particularly prominent at sites of contact between axon s and glial-cell processes. During remyelination (which in this lesion is accomplished predominantly by Schwann cells) the proportion of the axonal surface exhibiting Ca2+-ATPase activity decreased in concert w ith the progressive thickening of the new myelin sheath. The non-myeli n forming plasmalemma of Schwann cells was positive for the Ca2+ ATPas e activity, but activity was abruptly lost at the site of compaction b etween the inner and outer leaflets of the forming myelin sheath. Ecto -ATPase activity is a property of some cell adhesion molecules, and it follows that the changes observed in the distribution of ATPase activ ity in this study may reflect changes in the axolemma which are import ant for the successful repair of the lesion by remyelination. The ATPa se activity may, for example, reflect the changing distribution of mol ecules important in aiding axo-glial recognition and the establishment of axo-glial contacts.