Model for focal demyelination of the spinal dorsal columns of transgenic MBP-LacZ mice by phototargeted ablation of oligodendrocytes

Focal demyelination models provide powerful tools to study demyelination an d remyelination in the central nervous system. In this report, we present a novel technique, which selectively targets oligodendrocytes within the spi nal cord of transgenic mice to produce focal demyelination. Transgenic mice expressing the E. coli LacZ (beta-galactosidase) gene from the myelin basi c protein promotor allowed for oligodendrocyte-specific cleavage of topical ly applied fluorescein-di-beta-galactopyranoside liberating photoactivatabl e fluorescein. Subsequent fluorescence illumination generated oxygen radica ls that oxidized a second exogenous substrate, 3-amino-9-ethylcarbazote, to form a toxic precipitate within oligodendrocytes. Histochemical staining o f the spinal cord dorsal columns 8 days following phototargeting revealed t hat the treated region no longer contained beta-galactosidasepositive cells . Focal demyelination of the dorsal columns was observed to a depth of 150 mu m in transverse semithin plastic sections. Numerous bundles of naked axo ns interspersed with myelin, debris-laden macrophages, and reactive astrocy tes were evident by electron microscopy. Remyelination of axons by both oli godendrocytes and invading Schwann cells was observed within the treated re gion 14 days after phototargeting. Newly generated oligodendrocytes were id entified within the demyelinated region by their incorporation of bromodeox yuridine. Thus, this novel focal demyelination protocol provides: (1) a met hod for selective targeted ablation of oligodendrocytes in vivo, (2) contro l over the extent of the demyelinated region, with (3) an environment that maintains its remyelination capacity. Phototargeted ablation of oligodendro cytes may therefore be a useful model for studying axon-glia interactions, axon regeneration within a demyelinated zone, and remyelination of axons. ( C) 2000 Wiley-Liss, Inc.