Journal of Neuroscience, Vol 6, 1748-1756, Copyright © 1986 by Society for Neuroscience
Microtubule-associated protein 2 (MAP2) is present in astrocytes of the optic nerve but absent from astrocytes of the optic tract
SC Papasozomenos and LI Binder
Using the peroxidase-antiperoxidase staining technique at the light- and
electron-microscope levels and two monoclonal antibodies against
microtubule-associated protein 2 (MAP2), we found that astrocytes located
at the periphery of the rat optic nerve were strongly stained, while those
in the central region were very weakly stained. MAP2 immunoreactivity was
present in astrocytes of the optic chiasm, but was absent from astrocytes
in the optic tract. Inside astrocytes, MAP2 immunoreactivity was excluded
from bundles of glial filaments. Treatment of animals with
beta,beta'-iminodipropionitrile (IDPN), which caused axonal atrophy,
enhanced the staining intensity of all optic nerve astrocytes. Axons and
oligodendrocytes remained unstained. Using PAGE and Western immunoblots, we
found that extracts from bovine optic nerve contained MAP2. Astrocytes in
any other region of the nervous system were negative for MAP2
immunoreactivity, except of the pituicytes and the astrocytes of the
fimbria of hippocampus. The optic nerve, neurohypophysis, and hippocampal
fimbria are white matter tracts that travel unsupported and free of
surrounding nervous tissue. These findings suggest that MAP2 is expressed
in astrocytes that are under excessive mechanical stress and further
indicate that MAP2 may function as a cytoskeletal rigidifying agent in
certain cells.