Heterogeneous distribution of glial cell marker proteins and of cell nucleus marker in the myelinated region of the normal rat optic nerve

Glial cells are critically important for maintenance of neuronal activity in the optic nerve. The present study documents the distribution of glial structure proteins (GFAP: glial fibrillary acidic protein; MBP: myelin basic protein), a glial functional protein (GS: glutamine synthetase), and of a cell nucleus marker (bisBenzimide) in the various myelinated regions of the normal rat optic nerve. Fourteen optic nerves from 12 male Sprague-Dawley rats were employed. Immunohistochemistry and confocal microscopy were used 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 with 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 with a significant difference in strength in 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 with a significant difference. The heterogeneous distribution of GFAP, GS, bisBenzimide, cell nuclei, and MBP-immunoreactive particles along the longitudinal plane may be an important functional adaptation that reflects the not 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 part is under a mildly pathological condition in the normal rat optic nerve.