Synaptophysin immunohistochemistry in the human cochlea.

Light microscopy and immunohistochemical analyses of a freshly prepared human cochlea, removed at meningioma skull base surgery, were performed with particular emphasis on synaptophysin (SY) reactivity. Synaptophysin, a 38-kDa glycoprotein, is one of the most abundant integral membrane proteins of small presynaptic vesicles and is a useful marker for sites of synaptic transmission of the efferent olivocochlear system in the cochlea. Following fixation and decalcification, cryosections of 30 microm were prepared. To introduce immunostaining, free-floating sections were exposed to monoclonal SY antibody. Positive SY immunostaining was solely restricted to the neural and sensory structures and did not include supporting cells of the organ of Corti. Dense reaction products were noted around the hair cells, especially at the basal portion of the inner and outer hair cells and their neural poles, as well as around the inner spiral bundle, tunnel spiral bundle, outer spiral bundle and upper tunnel crossing fibers. The majority of spiral ganglion cells stained positively. An intermingling network of thin unmyelinated nerve fibers stained densely, especially at the basal portions of the cochlea. The spiral limbus, inner and outer sulcus cells, basilar membrane, myelinated nerve fibers, spiral ligament and the stria vascularis were unstained. Human cochlea obtained during surgery offers excellent conditions for immunohistochemical analysis. In the basal cochlea in the organ of Corti, outer hair cell area, there may be alterations due to noise trauma from the drilling procedure.