THE LOCALIZATION OF SYNAPTOPHYSIN IN THE ORGAN OF CORTI OF THE HUMAN AS SHOWN BY IMMUNOELECTRON MICROSCOPY

Synaptophysin, or p38, a polypeptide of molecular weight 38 kD, is a c alcium-binding membrane protein found in synaptic vesicles of neurons and smooth surfaced vesicles of neuroendocrine cells. Six human neonat al and infant temporal bones were fixed in paraformaldehyde and glutar aldehyde, decalcified in EDTA and were then immunoreacted for synaptop hysin (ICN Biomedicals) using the avidin-biotin reaction (ABC kit, Vec tor Labs). The tissue was then prepared for light microscopic surface preparation, radial sections of 5 microns, and serial section electron microscopy. At a light microscopic level, the inner spiral bundle, tu nnel spiral bundle, upper tunnel crossing fibers and the base of outer hair cells were stained. At the base of outer hair cells, the immunor eactivity was seen to decrease from the base to the apex and from the first to third outer hair cells. At an electron microscopic level, imm unoreactivity at the base of outer hair cells was limited to vesiculat ed efferent fibers. The degree of immunoreactivity between adjacent ef ferent fibers varied significantly. Immunoreactive vesiculated endings were also found in the supranuclear region of outer hair cells.