Comparison of demyelination and neural degeneration in spiral and Scarpa's ganglia of C57BL/6 mice.

Spiral and Scarpa's (vestibular) ganglia of female C57BL/6 mice, ranging in age from 1.5 to 32 months, were examined by light and electron microscopy. The spiral ganglia of C57BL/6 mice undergo sweeping neuronal losses. Based on cytological characteristics that repeat themselves in both young and old mice, we divided perikaryal demyelination and degeneration of spiral ganglia into four arbitary stages: 1) incipient demyelination, myelin sheaths begin to loosen and unravel; 2) contact, the partially demyelinated perikarya abut as the extracellular matrix disappear; 3) clumping, clusters of naked perikarya clump together, cytoplasmic processes surround the exterior of the clump; and 4) resorption, the clumps gradually disintegrate, leaving at completion large, fluid-filled spaces and few cellular remnants. In Scarpa's ganglia, a small number of neurons demyelinate and clump, but none degenerate or undergo resorption.