The astrocyte-extracellular matrix complex in CNS myelinated tracts: a comparative study on the distribution of hyaluronate in rat, goldfish and lamprey

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Abstract
The localization of hyaluronate was studied in the CNS of rat, goldfish and lamprey. Cryostat sections were incubated with glial hyaluronate-binding protein of human origin and stained by indirect immunofluorescence with glial hyaluronate binding protein antibodies not reaching with rat and fish. As previously reported for glial hyaluronate-binding protein and glial fibrillary acidic protein, hyaluronate and glial fibrillary acidic protein had a similar distribution in rat spinal cord and optic nerve, both substances forming ring-like structures around individual myelinated axons. A similar periaxonal distribution was observed in goldfish spinal cord and medulla, except that the rings were much wider, to accommodate the large goldfish axons. The glial fibrillary acidic protein-positive neuroglial tissue forming distinctive structures in goldfish vagal lobes also stained for hyaluronate. In both rat and goldfish spinal cord, motoneurons were surrounded by a hyaluronate coat. Goldfish optic nerve and lamprey spinal cord were hyaluronate-negative and, as previously reported, they stained for keratin but not for glial fibrillary acidic protein. The findings suggest that hyaluronate in CNS fibre tracts in a product of glial fibrillary acidic protein-positive neuroglia. They also suggest that the appearance of glial fibrillary acidic protein-positive neuroglia and the formation of a hyaluronate-bound extracellular matrix are related phenomena in phylogeny.