The heterogeneous distribution of glial cell marker proteins in the myelinated region of the normal rat optic nerve

Glial cells play a critical role in the maintenance of neuronal activity in the optic nerve. The present study reports the distribution of glial structural proteins (GFAP: glial fibrillary acidic protein; MBP: myelin basic protein), a glial functional protein (GS: glutamine synthetase), and of a cell nuclear marker (bisBenzimide) in the various myelinated regions of the normal rat optic nerve. Fourteen optic nerves from 12 male Sprague-Dawley rats were used. Immunohistochemistry and confocal microscopy were employed to investigate the distribution of GFAP, MBP, GS, and of bisBenzimide along the longitudinal plane of the myelinated region. GFAP-immunoreactivity and GS-immunoreactivity were strong in the distal (anterior)-most part but weak in the proximal (posterior) part, demonstrating a significant decrease in strength along the longitudinal plane of the myelinated region. bisBenzimide labeling was also strong in the distal-most part but weak in the proximal part, indicating a significant difference in strength across the myelinated region. MBP-immunoreactive particles and cell nuclei were densely distributed in the distal-most part; however, they were sparsely dispersed in the proximal part, showing a significant difference. The heterogeneous distribution of GFAP, GS, bisBenzimide, cell nuclei, and of MBP-immunoreactive particles along the longitudinal plane may represent an important functional adaptation reflecting the non-uniform nature of the physiological and structural environment of the myelinated region. Notably, the concentrations of GFAP, GS, and of MBP-immunoreactive particles in the distal-most part of the myelinated region suggest that this area is under physiologically stressed conditions in the normal rat optic nerve.