Intermediate cells detected in electron microscopic observation of the rat spiral ganglion

Morphological features of the rat spiral ganglion cells were investigated in serial sections by electron microscopy. Materials were obtained from healthy rat temporal bones after perfusion with glutaraldehyde. Cochleas were removed and prepared by routine electron microscopic methods. EDTA was used for decalcification. When semithin sections were studied two distinct types of the neurons were observed, the large and the small cell bodies, which were mostly myelinated. The differences between the organelles of these two cell type were analyzed under electron microscope. The large cell bodies were rich in cytoplasmic organelles and intracytoplasmic microfilaments were sparse. The small neurons contained fewer cytoplasmic organelles and were rich in microfilaments. In addition to the known types of neurons, higher magnifications indicated 1-2% of all these cells were intermediate cells. The morphological structure was basically the same as that of the large neurons but they were rich in cytoplasmic organelles including the microfilaments.