Age-related changes in MBP expression in the CBA/CaJ mouse spiral ganglion.

<p><b>A:</b> MBP⁺ myelin sheaths (green) enclose type I SGNs in Rosenthal's canal of the basal turn of a one month-old mouse. Intact MBP⁺ myelin sheaths (asterisks) are seen enveloping most neurons. Propidium iodide (PI) nuclear counterstaining (red) reveals nuclear profiles of both SGNs and Schwann cells. SGNs are identifiable by their larger, more weakly stained spherical nuclei whereas the nuclei of Schwann cells are recognized by their irregular shape and more intense staining. <b>B, C:</b> Abnormalities in MBP expression patterns in Rosenthal's canal of aged mice. Numerous SGNs are enclosed only partially by a MBP⁺ myelin sheath (arrows) and some SGNs appear to lose their MBP⁺ myelin sheath. Asterisks indicate two SGNs with normal-looking MBP⁺ myelin sheaths. <b>D, E:</b> Confocal images of myelin sheaths enveloping neurons from young (<b>D</b>) and aged (<b>E</b>) mice. Intact MBP⁺ myelin sheaths are indicated by asterisks while broken MBP⁺ myelin sheaths are indicated by white arrows. <b>F:</b> Quantitative analysis of SGNs with intact MBP⁺ myelin sheaths in young and aged mouse ears. The MBP⁺ myelin sheath was considered intact if it enclosed more than 80% of the outline of the perikarya. A significant decline in the percentage of intact MBP⁺ myelin sheath was found in all three cochlear turns in the aged mouse ears compared to young controls (n = 5–7 per group; <i>P</i><0.01; asterisk). Scale bar, 10 µm in <b>C</b> (applies to <b>A–C</b>); 10 µm in <b>E</b> (applies to <b>D–E</b>).