KAWANO, J. | bioRxiv Science

bioRxiv2025

Concentration of myelin debris-like myelin basic protein-immunoreactive particles in the distal (anterior)-most part of the myelinated region in the normal rat optic nerve

In the present study, we report that the concentration of myelin debris-like myelin basic protein-immunoreactive particles was observed in the distal (anterior)-most part of the myelinated region in the normal rat optic nerve. These particles were visualized using fluorescent immunohistochemistry with a mouse monoclonal anti-human myelin basic protein (MBPh) antibody (clone SMI-99). Fluorescent double immunohistochemistry, employing both the rat monoclonal anti-cow myelin basic protein (MBPc) antibody (clone 12) and the anti-MBPh antibody, revealed that the myelin basic protein immunoreactive-particles detected by the anti-MBPc antibody nearly completely overlapped with those immunostained by the anti-MBPh antibody. Since these antibodies target different sites, it can be concluded that these particles contain authentic myelin basic protein. We hypothesized that the MBPh-immunoreactive particles represent myelin debris-like structures in the normal rat optic nerve. Quantitative morphological analyses indicated that only 2 out of 6 differences in size and shape descriptors between the particles and the myelin debris observed in the damaged optic nerve of the glaucoma rat were statistically significant. Glial fibrillary acidic protein-immunoreactivity and glutamine synthetase-immunoreactivity were observed in the particles. Most of these particles were isolated from ionized calcium-binding adapter molecule 1-labeled microglia. These findings demonstrate that the myelin debris-like MBPh-immunoreactive particles are concentrated in the distal-most part of the myelinated region. This evidence suggests that the distal-most part is under physiologically stressed conditions. Furthermore, these findings may provide valuable insights into the pathophysiological mechanisms that induce localized vulnerability of the myelin sheaths. Key pointsO_LIThis article demonstrates that myelin basic protein-immunoreactive particles are densely distributed in the distal (anterior)-most part of the myelinated region in the normal rat optic nerve. C_LIO_LIThese particles exhibit morphological characteristics akin to myelin debris observed in the damaged optic nerve of the glaucoma rat. (45 words) C_LI Graphical Abstract Image O_FIG O_LINKSMALLFIG WIDTH=148 HEIGHT=200 SRC="FIGDIR/small/643597v2_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@13d6c62org.highwire.dtl.DTLVardef@1969690org.highwire.dtl.DTLVardef@176fd11org.highwire.dtl.DTLVardef@e08fd9_HPS_FORMAT_FIGEXP M_FIG C_FIG

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bioRxiv2025

Heterogeneous distribution of glial cell marker proteins and of cell nucleus marker 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. Key pointsO_LIThe present study reports the distribution of glial structural proteins (GFAP: glial fibrillary acidic protein; MBP: myelin basic protein), and of a glial functional protein (GS: glutamine synthetase) in the various myelinated regions of the normal rat optic nerve. C_LIO_LIGFAP-immunoreactivity and GS-immunoreactivity were strong in the distal (anterior)-most part but weak in the proximal (posterior) part. C_LIO_LIMBP-immunoreactive particles were densely distributed in the distal-most part; however, they were sparsely dispersed in the proximal part. C_LIO_LIThese results suggest that the distal-most part is not under physiological but rather under physiologically stressed conditions in the normal rat optic nerve. C_LI Graphical AbstractThe present study reports the distribution of glial structural pro-teins (GFAP: glial fibrillary acidic protein; MBP: myelin basic protein), and of a glial functional protein (GS: glutamine syn-thetase) in the various myelinated regions of the normal rat optic nerve. GF AP-immunoreactivity and GS-immunoreactivity were strong in the distal (anterior)-most part but weak in the proximal (poste-rior) part. MBP-immunoreactive particles were densely distributed in the distal-most part; however, they were sparsely dispersed in the proximal part. These results suggest that the distal-most part is not under physi-ological but rather under physiologically stressed conditions in the normal rat optic nerve. O_FIG O_LINKSMALLFIG WIDTH=197 HEIGHT=200 SRC="FIGDIR/small/643607v2_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@54c666org.highwire.dtl.DTLVardef@1ad8f3borg.highwire.dtl.DTLVardef@196870borg.highwire.dtl.DTLVardef@17c1641_HPS_FORMAT_FIGEXP M_FIG C_FIG

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