Three-dimensional observation of the spiral ganglion cell. Normal structure and pathological changes

Spiral ganglia of guinea pig and mouse were investigated by scanning electron microscopy (SEM). The cochlea was freeze-fractured and then macerated with 0.1% OsO4 solution for 70-90 h (A-O-D-O method (1]. This allowed three-dimensional observation of the general view of the spiral ganglion and the intracellular structure. Two types of spiral ganglion cell, type I and type II, could be distinguished by the A-O-D-O method. Intracellular membranous structures such as mitochondria, endoplasmic reticulum (ER) and Golgi apparatus were also demonstrated stereoscopically. Furthermore, morphological changes in mouse spiral ganglion cells due to injection of Mycobacterium fortuitum were observed, using SEM. The degenerative process began as swelling of the mitochondria. When Schwann cell became affected, the myelin sheath disappeared and the ganglion cell border became indistinct. This degeneration developed rapidly, suggesting a direct influence of the bacteria on the ganglion cell. Various types of inclusion body with limiting membrane could be demonstrated stereoscopically. As Romand & Romand (4) suggested, these inclusion bodies may be remnants of cellular organellae or various type of lysosomes.